Close Quarters Battle. Combat occuring in close quarters, such as indoors, streets and ally-ways where surroundings severely limits maneuverability and visibility to the point where standard methods, equipment and tactics are no longer suitable.
SWAT teams, are among the best examples of CQB operations, as they are highly trained to work in narrow, restrictive and confusing environments, using tactics which are very different to that of military infantry trained to operate in more open environments.
CQB is a modern term used to define combat using firearms and special CQB equipment. Generally, SOPs (standard Operating Procedures) for CQB never involve hand to hand combat and CQB operatives are highly trained with firearms at close to point blank conditions.
Do not be confused with the term CQB used in Metal Gear Solid Snake Eater, which is a fictional use of the term to describe a form of martial art invented by Snake(Big Boss) and the Boss.