Singularity: The center of a black hole, where the curvature of space-time is maximal. At singularity, the gravitational tides deviate; no solid object can yet theoretically survive beating the singularity. Though singularities usually predict inconsistencies in theory, singularities in the black holes do not essentially entail that general relativity is unfinished so long as singularities are always bounded by the event horizons.
The proper formulation of quantum gravity might well avoid the traditional singularity at the centers of the black holes.