A bomb is an explosive device which generates a violent shock wave, and is usually some kind of container filled with explosive material, designed to cause random destruction when set off. The explosion of the bomb has to be triggered, usually by a clock, a remote control, or some kind of sensor, usually pressure (altitude), radar, or contact. The word comes from the Greek âüìâïò (bombos), an onomatopoetic term with approximately the same meaning as "boom" in English.

These are first and foremost weapons; the term "bomb" is not usually applied to explosive devices used for civilian purposes (such as construction or mining). Note that many military explosive devices are not called "bombs". The military mostly calls airdropped, unpowered explosive weapons "bombs," and such bombs are usually the provenance of air forces and naval aviation. Other military explosive devices are called grenades (such as hand grenades), shells, depth charges, missiles or mines.

They have been used for centuries in warfare and are a central part of the terrorist's arsenal. They fall into three distinct categories: conventional (filled with chemical explosives), dispersive (filled with submunitions, chemicals or other disruptive agents which are spread on or shortly before impact) or nuclear (relying on nuclear fission or nuclear fusion for their effect).

A distinction is commonly drawn between terrorist and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, terrorist bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, they are generally referred to as improvised explosive devices or IEDs.

The most powerful bomb in existence is the hydrogen bomb, a nuclear weapon. The most powerful non-nuclear bomb is the United States Air Force's MOAB (Massive Ordnance Air Burst).