Question

Who knows what an Event Horizon is?

Answer 1

In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms, it is defined as the shell of "points of no return", i.e., the points at which the gravitational pull becomes so great as to make escape impossible, even for light.

Answer 2

A theoretical boundary around a black hole beyond which no light or other radiation can escape.