Final answer:
The center of a black hole, where matter is thought to be infinitely dense and compressed to a point of zero volume, is called a singularity. It's different from the event horizon, which is the black hole's boundary that nothing can cross and escape from once inside.
Step-by-step explanation:
The place at the center of a black hole where, in principle, gravity crushes all matter to an infinitely tiny and dense point is called a singularity. This is a region of space where the density is thought to be infinite and the volume zero, fundamentally challenging our understanding of physics as it currently stands. While the event horizon is the 'point of no return' surrounding this singularity, where the escape velocity equals the speed of light and nothing, not even light, can escape from within it, it is not the singularity itself. In contrast, a quasar is a highly luminous and active galactic nucleus powered by a supermassive black hole, and a pulsar is a rapidly spinning neutron star that emits beams of electromagnetic radiation.