What are black holes?

For a while now, I have gathered a sudden interest in space. One of my questions are:                                 What are black holes?

 In this article which I have found, it explains everything you need to know about this certain subject. 

Simply put, a black hole is a region of space that is so incredibly dense that not even light can escape from the surface. However, it is this fact that often leads to miss-understanding. Black holes, strictly speaking, don't have any greater gravitational reach than any other star of the same mass. If our Sun suddenly became a black hole of the same mass the rest of the objects, including Earth, would be unaffected gravitationally. The Earth would remain in its current orbit, as would the rest of the planets. (Of course other things would be affected, such as the amount of light and heat that Earth received. So we would still be in trouble, but we wouldn't get sucked into the black hole.)

There is a region of space surrounding the black hole from where light can not escape, hence the name. The boundary of this region is known as the event horizon, and it is defined as the point where the escape velocity from the gravitational field is equal to the speed of light. The calculation of the radial distance to this boundary can become quite complicated when the black hole is rotating and/or is charged.

For the simplest case (a non-rotating, charge neutral black hole), the entire mass of the black hole would be contained within the event horizon (a necessary requirement for all black holes). The event horizon radius (Rs) would then be defined as Rs = 2GM/c2.