1. In astrophysics, the point in space-time at which the known laws of physics break down.

Singularity is predicted to exist at the center of a black hole, where infinite gravitational forces compress the infalling mass of a collapsing star to infinite density.

It is also, according to the Big Bang model of the origin of the universe, to be the point from which the expansion of the universe began.

2. A point in space at which an infinitely strong gravitational field exists.

Such a concept is predicted by general relativity to exist at the center of a black hole.