An intermediate-range ballistic missile (IRBM) is a ballistic missile with a range of 3,000–5,500 km, between a medium-range ballistic missile (MRBM) and an intercontinental ballistic missile (ICBM). Classifying ballistic missiles by range is done mostly for convenience. In principle there is very little difference between a low-performance ICBM and a high-performance IRBM, because decreasing payload mass can increase the range over the ICBM threshold. The range definition used here is used within the U.S. Missile Defense Agency.

A ballistic missile (BM) is a type of missile that uses projectile motion to deliver warheads on a target. These weapons are powered only during relatively brief periods—most of the flight is unpowered. Short-range ballistic missiles (SRBM) typically stay within the Earth's atmosphere, while most larger missiles are exo-atmospheric. The largest ICBMs are capable of full orbital flight. These weapons are in a distinct category from cruise missiles, which are aerodynamically guided in powered flight and thus restricted to the atmosphere.