Finally something. Time dilation is where time speeds up/slows down depending on the speed you are travelling through space relative to an observer. Put simply, if two identical twins, A and B started off on Earth. Twin A flies around the galaxy for a few years at a significant fraction of the speed of light. Twin B stays on Earth. When the meet up again, twin A will be younger than twin B. Moreover, if twin A had looked into B’s spaceship as it went past then A would appear to move in slow motion as time flows slower on the ship!

Mind bending eh!