Answer:
Black hole is described by singularity of Schwarzchild's equation.
Step-by-step explanation:
Einstein's field equations consists of 10 sets of equations describing general relativity: Space time curves in presence of mass and energy.

Condition of black-hole came from Schwarzchild's solution to Einstein's field equation:

Black hole is described by singularity of Schwarzchild's equation.

It defines the event horizon of the Schwarzchild's black-hole.