A time bomb is usually an improvised explosive device comprising a battery, detonator, an explosive charge, and a timer (often prepared from some sort of alarm clock) which substitutes for a fuse or trigger. Depending upon the design, the bomb can be set to detonate any time between a few minutes and several days after it has been secreted within the target area.

The term can also refer to a self-executing file saved in a hidden directory on a computer system which will cause massive damage to other saved files.

As a figure of speech, the term "time bomb" refers to a situation where the danger is increasing and there is a point in time where the situation becomes "explosive" or disastrous.