Black Hole is a term coined by John Wheeler in the year 1967, while presiding over a meeting at the Space Institute. He used this term to refer to stars which have completely collapsed. A collapse of a star happens when the mass of the star becomes thrice the mass of sun. The star tends to become more and more compact and so dense that it even defies gravity and the light passing through it. This causes the object to be pitch dark and hinders the viewing of the star directly. Hence the term Black Hole was used to refer to such collapsed stars.