A bomb is an explosive device, usually some kind of container, filled with explosive material, designed to cause 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.
Bombs are often used in warfare, and by terrorists. The most powerful bomb in existence is the hydrogen bomb.
Bomb is a slang word for a lot of money.
Bomb is also used in the sense of going very quickly.