Time dilation refers to:?

A the slowing of time of a moving clock as measured by observer considered to be at rest
B increasing time factors as one's speed increases
C the slowing of time of a moving clock as measured by the moving clocks
D the illusion of relative time between moving and non moving clocks

I think its a but can not find any information about this

3 answers

A is correct.
Time dilation is the theory of time relative to motion. It is the principle that time elapsed is relative to motion, such that time passes more slowly for a system in motion than for one at rest relative to an outside observer. Further, as predicted by Einstein's special theory of relativity, time passes increasingly slowly as the motion relative to the observer approaches the speed of light.
It is more than a theory, Alice, it has been demonstrated in experiment and observations many times.