What is Event Horizon?

In general relativity, event horizon is a general term for a boundary in spacetime, defined with respect to an observer, beyond which events cannot affect the observer. Light emitted beyond the horizon can never reach the observer, and anything that passes through the horizon from the observer's side is never seen again. taken from http://en.wikipedia.org/wiki/Event_horizon

It is actually a point beyond which the escape velocity becomes equal or greater than light.It is encountered during the formation of a Black Hole

WOW. I learned something new today! I knew about the black hole, but this term in connection with it is totally new!

dont knw..