A black hole is a region of space that has so much mass concentrated in it that there is no way for a nearby
object to escape its gravitational pull. Since our best theory of gravity at the moment is Einstein's general theory of relativity, we have to delve into some results of this theory to understand black holes in detail, but let's not.. :) perhaps I will find some way of posting this one REALLY long report I wrote once on why we think that black holes exist.. since they are dark matter and we must rely on indirect methods of detection.. yeah!