Nuclear Glossary
Key terms in nuclear security, arms control, military strategy, and the Iran crisis — defined in plain language.
46 terms. Search or scroll to browse. Terms link to each other for easy cross-reference.
A
- Arms Control
- Agreements between nations to limit the development, production, stockpiling, proliferation, and usage of weapons, particularly weapons of mass destruction. Key treaties include New START, the INF Treaty, and the Comprehensive Nuclear-Test-Ban Treaty (CTBT).
- Related: nonproliferation, new start, npt, jcpoa
- See also: How Nuclear Deterrence Works, Russia vs United States Nuclear Comparison
- Article II Powers
- The constitutional authority of the US President as Commander-in-Chief under Article II of the Constitution. Presidents have invoked Article II to authorize military action without explicit Congressional approval, including the 2026 strikes against Iran under Operation Epic Fury.
- Related: aumf, war powers resolution
- See also: What Is an AUMF?, US Military Buildup — Operation Epic Fury
- AUMF
- Authorization for Use of Military Force. A joint resolution passed by Congress that authorizes the President to use military force against specific targets. The 2001 AUMF (targeting al-Qaeda) and 2002 AUMF (targeting Iraq) have been controversially cited to justify operations far beyond their original scope, including Operation Epic Fury against Iran.
- Related: war powers resolution, article ii powers
- See also: What Is an AUMF?
- Axis of Resistance
- An Iran-led coalition of state and non-state actors opposed to US and Israeli influence in the Middle East. Core members include Hezbollah (Lebanon), the Houthis (Yemen), Iraqi Shia militias (including Kata'ib Hezbollah and the Popular Mobilization Forces), and Syrian government forces. The network provides Iran with strategic depth and asymmetric escalation options.
- Related: irgc, quds force, proxy war
- See also: What Are Proxy Wars?, Iran Retaliatory Strikes on US Bases
B
- Blockade
- A military operation to prevent the passage of vessels, aircraft, or goods into or out of an area. Iran's closure of the Strait of Hormuz in 2026 constitutes a naval blockade affecting approximately 20% of global oil supply. Under international law, a blockade is considered an act of war.
- Related: strait of hormuz, chokepoint
- See also: What Is the Strait of Hormuz?
- Breakout Time
- The estimated time a country would need to produce enough weapons-grade fissile material (highly enriched uranium or plutonium) for a single nuclear weapon, starting from its current enrichment level. Iran's breakout time was estimated at less than two weeks before the 2026 strikes, down from over 12 months under the JCPOA.
- Related: enrichment, heu, fissile material, jcpoa
- See also: What Is Nuclear Breakout Time?, Iran vs North Korea Nuclear Comparison
- Bulletin of the Atomic Scientists
- An academic journal and nonprofit organization founded in 1945 by former Manhattan Project scientists. They maintain the Doomsday Clock and publish expert analysis on nuclear risk, climate change, and disruptive technologies. The Bulletin's Science and Security Board sets the clock position annually.
- Related: doomsday clock
- See also: What Is the Doomsday Clock?
C
- Carrier Strike Group
- A US Navy formation centered on an aircraft carrier, typically including guided-missile cruisers, destroyers, a submarine, and a supply ship. Each carrier can deploy 70+ combat aircraft. Two carrier strike groups were deployed to the Persian Gulf for Operation Epic Fury, representing the largest naval concentration in the region since the 2003 Iraq War.
- Related: nuclear triad, force projection
- See also: US Military Buildup — Operation Epic Fury
- Centrifuge
- A machine that spins uranium hexafluoride gas at extremely high speeds to separate the fissile isotope uranium-235 from the more common uranium-238. Cascades of thousands of centrifuges are required for enrichment. Iran operated advanced IR-6 and IR-9 centrifuges at Fordow and Natanz before the 2026 strikes.
- Related: enrichment, breakout time, heu
- See also: What Is Nuclear Breakout Time?, What Happens if Iran Gets Nuclear Weapons?
- Chokepoint
- A narrow geographic passage through which maritime traffic must pass, creating a strategic vulnerability. The Strait of Hormuz (21 miles wide, 20% of global oil) and Bab el-Mandeb (18 miles wide, 12% of global trade) are the two most critical chokepoints affected by the 2026 conflict.
- Related: strait of hormuz, blockade
- See also: What Is the Strait of Hormuz?
D
- De-mated
- A nuclear weapons posture in which warheads are stored separately from their delivery vehicles (missiles, aircraft) during peacetime. India and Pakistan keep their arsenals de-mated, requiring assembly and mounting before use. This posture reduces the risk of accidental launch but increases response time.
- Related: deterrence, no first use
- See also: India vs Pakistan Nuclear Comparison, How Nuclear Deterrence Works
- Deterrence
- A military strategy in which one nation uses the threat of nuclear retaliation to discourage an attack by an adversary. Effective deterrence requires a credible second-strike capability and the perceived willingness to use nuclear weapons. The concept underpins the nuclear postures of all nine nuclear-armed states.
- Related: mutual assured destruction, first strike, second strike, no first use
- See also: How Nuclear Deterrence Works, What Is Mutually Assured Destruction?
- Doomsday Clock
- A symbol created by the Bulletin of the Atomic Scientists in 1947 that represents the likelihood of a human-made global catastrophe, with midnight symbolizing the end of civilization. Set at 89 seconds to midnight as of January 2025 — the closest it has ever been. NukeClock's live estimate incorporates real-time events.
- Related: bulletin of the atomic scientists
- See also: What Is the Doomsday Clock?, Today's Assessment
E
- Enrichment
- The process of increasing the concentration of the fissile isotope uranium-235 in uranium. Natural uranium contains 0.7% U-235. Low-enriched uranium (LEU, below 20%) is used for power reactors. Highly enriched uranium (HEU, 90%+) is weapons-grade. Iran enriched to 60% before the 2026 strikes — a level with no civilian application.
- Related: centrifuge, breakout time, heu, leu, fissile material
- See also: What Is Nuclear Breakout Time?, Iran vs North Korea Nuclear Comparison
F
- First Strike
- A preemptive nuclear attack intended to destroy an adversary's nuclear arsenal and command structure before they can retaliate. The fear of first strikes drives nuclear arms races, early warning systems, and the maintenance of second-strike capabilities. Operation Epic Fury's strikes on Iran's nuclear facilities represent a conventional first strike against nuclear infrastructure.
- Related: deterrence, second strike, no first use
- See also: How Nuclear Deterrence Works, Nuclear Threat Assessment: What Happens Next
- Fissile Material
- Material capable of sustaining a nuclear chain reaction. The two primary fissile materials used in nuclear weapons are highly enriched uranium (HEU) and plutonium-239. North Korea is estimated to produce enough fissile material for 6–18 warheads per year.
- Related: enrichment, heu, breakout time
- See also: What Is Nuclear Breakout Time?, Who Has the Most Nuclear Weapons?
- Force Projection
- The ability of a nation to deploy and sustain military forces outside its territory. The United States has unmatched force projection capability through its global network of military bases, carrier strike groups, and strategic airlift capacity. Operation Epic Fury required force projection across 8 host nations.
- Related: carrier strike group
- See also: US Military Buildup — Operation Epic Fury
G
- GBU-57
- The Massive Ordnance Penetrator (MOP), a 30,000-pound precision-guided bunker buster bomb designed to destroy hardened underground targets. Delivered exclusively by B-2 Spirit stealth bombers. Used against Iran's Fordow enrichment facility — built inside a mountain — in the opening strikes of Operation Epic Fury. The first combat use of the weapon's full penetration capability.
- Related: enrichment
- See also: Iran Supreme Leader Khamenei Killed in US-Israeli Strikes, US Military Buildup — Operation Epic Fury
H
- HEU
- Highly Enriched Uranium. Uranium enriched to 20% or above concentration of the U-235 isotope. Weapons-grade HEU is enriched to 90% or above. Producing HEU is the most technically challenging step in building a uranium-based nuclear weapon.
- Related: enrichment, leu, breakout time, fissile material
- See also: What Is Nuclear Breakout Time?
I
- IAEA
- The International Atomic Energy Agency. A UN-affiliated organization headquartered in Vienna that promotes the peaceful use of nuclear energy and monitors compliance with the Non-Proliferation Treaty through inspections and safeguards. The IAEA has been denied access to Iranian nuclear facilities since the 2026 strikes.
- Related: npt, nonproliferation, jcpoa
- See also: What Is the IAEA?, IAEA Iran Nuclear Facilities Access Blocked
- ICBM
- Intercontinental Ballistic Missile. A long-range (over 5,500 km) ballistic missile typically designed to deliver nuclear warheads. Part of the nuclear triad alongside SLBMs and strategic bombers. The US operates 400 Minuteman III ICBMs; Russia fields approximately 300 ICBMs including the RS-28 Sarmat; China has built 300+ new ICBM silos.
- Related: nuclear triad, slbm, mirv
- See also: Who Has the Most Nuclear Weapons?, Russia vs United States Nuclear Comparison
- IRGC
- The Islamic Revolutionary Guard Corps. A branch of Iran's armed forces founded after the 1979 revolution, operating parallel to the regular military. The IRGC controls Iran's ballistic missile program, overseas covert operations (via the Quds Force), and significant economic interests. Designated as a foreign terrorist organization by the United States.
- Related: quds force, axis of resistance
- See also: Iran Retaliatory Strikes on US Bases, Iran vs Israel Military Power
- Iron Dome
- An Israeli mobile air defense system designed to intercept short-range rockets and artillery shells with a range of 4–70 km. Developed by Rafael Advanced Defense Systems and deployed since 2011. During the 2026 conflict, Iron Dome was pushed to operational limits by Hezbollah's sustained rocket barrages.
- Related: thaad, patriot
- See also: Iran vs Israel Military Power, Can the US Shoot Down a Nuclear Missile?
J
- JCPOA
- The Joint Comprehensive Plan of Action, commonly known as the Iran nuclear deal. Signed in 2015 between Iran and six world powers (US, UK, France, Germany, Russia, China), it limited Iran's enrichment to 3.67% and extended breakout time to 12+ months in exchange for sanctions relief. The US withdrew in 2018; Iran subsequently exceeded all enrichment limits.
- Related: enrichment, breakout time, iaea, arms control
- See also: Geneva Nuclear Negotiations Collapse, What Happens if Iran Gets Nuclear Weapons?
L
- LEU
- Low-Enriched Uranium. Uranium enriched to below 20% concentration of the U-235 isotope, typically 3–5% for use in civilian power reactors. The JCPOA limited Iran to 3.67% enrichment. LEU cannot be used directly in a nuclear weapon but can be further enriched to weapons-grade.
- Related: enrichment, heu, jcpoa
- See also: What Is Nuclear Breakout Time?
M
- MIRV
- Multiple Independently targetable Reentry Vehicle. A missile payload containing multiple nuclear warheads, each capable of striking a different target. MIRVed missiles multiply the effective striking power of a single missile. China's DF-41 carries up to 3 MIRVs; Russia's RS-28 Sarmat can carry 10+.
- Related: icbm, slbm, nuclear triad
- See also: Who Has the Most Nuclear Weapons?, Russia vs United States Nuclear Comparison
- Mutual Assured Destruction
- A doctrine of military strategy (abbreviated MAD) in which a full-scale use of nuclear weapons by an attacker would result in the complete annihilation of both the attacker and the defender. MAD was the dominant framework of US-Soviet nuclear relations during the Cold War and remains the foundation of strategic stability between the US and Russia.
- Related: deterrence, first strike, second strike
- See also: What Is Mutually Assured Destruction?, How Many Nukes to Destroy the World?
N
- NEW START
- The New Strategic Arms Reduction Treaty between the US and Russia, signed in 2010, limiting each country to 1,550 deployed strategic nuclear warheads and 700 deployed delivery systems. Russia suspended participation in 2023 and the treaty's verification mechanisms are no longer operational, removing a key guardrail on the world's two largest arsenals.
- Related: arms control, nonproliferation, icbm
- See also: Russia vs United States Nuclear Comparison, How Nuclear Deterrence Works
- No-First-Use
- A nuclear doctrine in which a state pledges not to use nuclear weapons unless first attacked by an adversary using nuclear weapons. China and India maintain no-first-use policies. Pakistan, Russia, the US, UK, and France explicitly reject NFU, reserving the right to use nuclear weapons first under certain conditions.
- Related: deterrence, first strike, de mated
- See also: India vs Pakistan Nuclear Comparison, How Nuclear Deterrence Works
- Nonproliferation
- Efforts to prevent the spread of nuclear weapons and weapons technology to nations that do not already possess them. The cornerstone is the NPT. The 2026 Iran strikes have complicated nonproliferation by demonstrating that nuclear programs are vulnerable to military attack — potentially accelerating proliferation by states seeking completed deterrents.
- Related: arms control, npt, iaea, jcpoa
- See also: Iran vs North Korea Nuclear Comparison, What Is the IAEA?
- NPT
- The Treaty on the Non-Proliferation of Nuclear Weapons, signed in 1968. Recognizes five nuclear-weapon states (US, Russia, UK, France, China) and prohibits non-nuclear states from acquiring weapons. India, Pakistan, Israel, and North Korea are not bound by the NPT. North Korea is the only state to have withdrawn (2003).
- Related: nonproliferation, arms control, iaea
- See also: What Is the IAEA?, Who Has the Most Nuclear Weapons?
- Nuclear Triad
- A three-pronged nuclear force structure consisting of land-launched ICBMs, submarine-launched ballistic missiles (SLBMs), and strategic aircraft carrying nuclear bombs or cruise missiles. The US, Russia, China, and India operate triads. The triad provides redundancy: even if two legs are destroyed in a first strike, the surviving leg ensures retaliation.
- Related: icbm, slbm, deterrence, second strike
- See also: Russia vs United States Nuclear Comparison, Who Has the Most Nuclear Weapons?
- Nuclear Umbrella
- A security guarantee in which a nuclear-armed state extends its nuclear deterrence to protect non-nuclear allied states. The US provides nuclear umbrellas to NATO allies, Japan, South Korea, and Australia. Nuclear umbrella commitments create extended deterrence but also raise questions about credibility — whether a state would risk its own cities to defend an ally.
- Related: deterrence, nuclear sharing
- See also: How Nuclear Deterrence Works
- Nuclear Sharing
- A NATO arrangement in which the United States stations tactical nuclear weapons (B61 gravity bombs) in allied countries. Host nations provide dual-capable aircraft and crews trained to deliver the weapons in wartime. Current host countries include Belgium, Germany, Italy, the Netherlands, and Turkey. Approximately 100 B61 bombs are forward-deployed in Europe.
- Related: nuclear umbrella, deterrence
- See also: How Nuclear Deterrence Works, Who Has the Most Nuclear Weapons?
P
- Patriot
- The MIM-104 Patriot is a US-made surface-to-air missile defense system designed to intercept tactical ballistic missiles, cruise missiles, and aircraft. The PAC-3 variant has been deployed to the Persian Gulf to defend US installations against Iranian missile attacks during Operation Epic Fury.
- Related: thaad, iron dome
- See also: Can the US Shoot Down a Nuclear Missile?
- Proxy War
- A conflict in which major powers support opposing sides — through funding, weapons, training, or direct military support — without engaging each other directly. Iran's use of Hezbollah, the Houthis, and Iraqi Shia militias to attack US and Israeli targets is the defining proxy warfare dimension of the 2026 crisis.
- Related: axis of resistance, quds force
- See also: What Are Proxy Wars?, Iran Retaliatory Strikes on US Bases
Q
- Quds Force
- The extraterritorial operations branch of Iran's Islamic Revolutionary Guard Corps (IRGC), responsible for foreign intelligence and covert military operations. The Quds Force manages Iran's relationships with proxy militias across the Middle East, including Hezbollah, the Houthis, and Iraqi Shia armed groups. Previously commanded by Qasem Soleimani until his assassination in January 2020.
- Related: irgc, axis of resistance, proxy war
- See also: What Are Proxy Wars?
S
- Sanctions
- Economic penalties imposed by one or more nations to pressure a target country into changing its behavior. Nuclear-related sanctions against Iran have targeted oil exports, banking, and technology transfers. Sanctions were partially lifted under the JCPOA (2015) and reimposed after the US withdrawal (2018).
- Related: jcpoa, nonproliferation
- See also: Iran vs North Korea Nuclear Comparison, Geneva Nuclear Negotiations Collapse
- Second Strike
- The assured ability of a country to respond to a nuclear attack with nuclear weapons of its own. Second-strike capability — typically provided by survivable submarine-based missiles — is considered essential for stable deterrence. Without it, an adversary might be tempted to launch a disarming first strike.
- Related: first strike, deterrence, slbm, nuclear triad
- See also: How Nuclear Deterrence Works, Russia vs United States Nuclear Comparison
- SIPRI
- The Stockholm International Peace Research Institute. An independent international institute founded in 1966 that researches conflict, armaments, arms control, and disarmament. SIPRI's annual Yearbook is the most widely cited source for global nuclear warhead estimates and military expenditure data.
- Related: arms control, nonproliferation
- See also: Who Has the Most Nuclear Weapons?
- SLBM
- Submarine-Launched Ballistic Missile. A ballistic missile carried on and launched from a submarine, typically a nuclear-powered ballistic missile submarine (SSBN). The US Trident II D5 and Russia's RSM-56 Bulava are current frontline SLBMs. SLBMs provide the most survivable leg of the nuclear triad.
- Related: nuclear triad, ssbn, icbm, second strike
- See also: Who Has the Most Nuclear Weapons?, How Nuclear Deterrence Works
- SPR
- Strategic Petroleum Reserve. The world's largest government-owned emergency crude oil stockpile, maintained by the US Department of Energy in underground salt caverns along the Gulf of Mexico coast. Holding approximately 400 million barrels, the SPR can be released to offset supply disruptions. Drawdowns were authorized in response to the Strait of Hormuz blockade.
- Related: strait of hormuz, blockade
- See also: What Is the Strait of Hormuz?
- SSBN
- A nuclear-powered ballistic missile submarine. SSBNs carry submarine-launched ballistic missiles (SLBMs) and provide the most survivable component of a nuclear triad because they are extremely difficult to track underwater. The US operates 14 Ohio-class SSBNs; Russia operates 11; the UK and France each operate 4; China operates 6 Jin-class SSBNs.
- Related: slbm, nuclear triad, second strike
- See also: Who Has the Most Nuclear Weapons?, Russia vs United States Nuclear Comparison
- Strait of Hormuz
- A narrow waterway (21 miles wide at its narrowest) between Iran and Oman connecting the Persian Gulf to the Gulf of Oman and the open ocean. Approximately 20% of global oil supply transits the strait daily. Iran closed the strait with naval mines, fast-attack boats, and anti-ship missiles on March 1, 2026, triggering the largest oil supply disruption since the 1973 Arab oil embargo.
- Related: chokepoint, blockade, spr
- See also: What Is the Strait of Hormuz?, Iran Retaliatory Strikes on US Bases
T
- THAAD
- Terminal High Altitude Area Defense. A US Army anti-ballistic missile defense system designed to intercept short-, medium-, and intermediate-range ballistic missiles during their terminal phase (descent). THAAD batteries were deployed to the Persian Gulf to protect US installations and allied infrastructure from Iranian missile attacks.
- Related: patriot, iron dome
- See also: Can the US Shoot Down a Nuclear Missile?
W
- War Powers Resolution
- A 1973 US federal law (also called the War Powers Act) requiring the President to notify Congress within 48 hours of committing armed forces to military action and prohibiting deployments longer than 60 days without Congressional authorization. Senator Tim Kaine introduced a War Powers Resolution vote in response to Operation Epic Fury.
- Related: aumf, article ii powers
- See also: What Is an AUMF?, US Military Buildup — Operation Epic Fury