blackhole

[chilli-pepa]

What exactly is a black hole

[Gnu]

It is a region of space where the matter is extremely dense (e.g. when all the mass of a star collapses into a very small volume). This distorts space-time to such an extent that light cannot escape from it, so it appears black.

[mibn2cweus]

Do you mean 'black hole' as in out there in space? Imagine the entire mass of the Earth contained within the size of one orange. Gravity would be so strong on the surface of this earth/orange that not even light could escape its gravitational field. This kind of black hole has a tendency to reveal more about what we don�t know about everything than what we do. So feel free to speculate so long as you don�t claim any first hand knowledge of what your taking about just as I don�t.

[Clanad]

And speculation by scientists seems to suggest that there are a lot of them... to the point that a belief is emerging that each galaxy has one at the center. Equations suggest that they are in various sizes, as well, from very small to unimagineably large....

[fo3nix]

I think the above answers have answered your question very well (for the basics), but here are some links to explanations with far more detail:

http://www.gothosenterprises.com/black_holes/
http://en.wikipedia.org/wiki/Black_hole

Don't let the science talk and maths in the latter link tie you down; you dont need it to understand what a black hole is.

[undercovers]

who hasn't taken of the unchanging front page of AB...

enough black hole info to fill even the largest boots

http://www.theanswerbank.co.uk/Article3471.html

[undercovers]

that was meant to say - who hasn't taken any notice of the unchanging front page of the answerbank?

[jimmer]

a black hole is a collapsed star. the gravitational force of the colapsed star pulls in everything close enough to it including light.

[Skids]

Its an 80s Disney film starring Robert Forster, Ernst Borgnine and a big scary robot called Maximillion.