Time dilation is the phenomenon in which time slows down for an observer inside a fast-moving object.
The idea of time dilation is not a new one. It was first proposed by Albert Einstein in his theory of relativity, and has been tested many times since then. The theory of relativity suggests that if you are traveling at the speed of light, your time would slow down relative to those who are stationary.
In the context of black holes, the closer you get to the event horizon, the slower time moves relative to those outside it. This means that if you were to fall into a black hole, your watch would tick slower than if you were standing on Earth's surface. This is due to gravitational time dilation - a change in how fast time passes as one approaches an object with gravity.