A black hole is literally a region from which light cannot escape.
General Relativity predicts that black holes can form by gravitational collapse. Once a star has burned up its supply of nuclear fuel, it can no longer support itself against its own weight and it collapses.
It will reach a critical density at which an explosive re-ignition of burning occurs, called a supernova.
COSMOS to HUMANITY, Spring 2008
Lecture 2 , slide 14