the principle predicted by relativity that time intervals between events in a system have larger values measured by an observer moving with respect to the system than those measured by an observer at rest with respect to it

The relativistic effect of the slowing of a clock with respect to an observer. In Special Relativity, a clock moving with respect to an observer appears to run more slowly than to an observer moving with the clock. In General Relativity, time dilation is also caused by gravity; clocks on the earth's surface, for example, run more slowly than clocks at high altitudes, where gravitational forces are weaker.

In physics, the apparent slowing down of moving clocks that is predicted by the special theory of relativity. Time dilation is well verified experimentally.