A black hole is a region of spacetime where gravity is so strong that nothing, not even light, can escape. These celestial objects form when massive stars exhaust their fuel and undergo gravitational collapse, causing matter to compress into an extremely dense singularity. The boundary around a black hole, known as the event horizon, marks the point of no return; anything crossing it is irrevocably pulled toward the singularity. While the formation process involves stellar remnants, the physical structure is defined by its event horizon and the underlying gravitational curvature of spacetime, making them critical subjects in modern physics and cosmology.