[moose07]

The point in the mouth of a Black hole where the gravity is so strong light cannot escape.
Hence you see nowt but black.
As far as i know ,only X-rays are emitted back from the Event Horizon.

[FredZarguna]

Yes, the event horizon is the radius below which the escape velocity is greater than the speed of light. Closer than that distance, and you don't get out.

X-Rays: Nothing comes back from the event horizon [well, because of Quantum Mechanics that's not quite true, but close enough.]

The X-rays "emitted from" Black Holes are actually the result of gravitational effects happening within a few thousands or millions of miles outside the event horizon. Here is one explanation: http://physics.stackexchange.com/questions/24958/how-can-a-black-hole-emit-x-rays. There are other reasons as well. But all of them are well beyond the event horizon.