What defines a black hole as a region of spacetime according to its gravitational property?

Gravity is so strong that nothing, not even light, can escape its boundary

A black hole represents the ultimate end state of gravitational collapse when the core mass exceeds approximately 3 solar masses, meaning no known physics can successfully counteract the inward pull of gravity. The defining characteristic of this resulting object is the extreme strength of its gravitational field within a specific boundary, known as the event horizon. Once matter or radiation, including photons of light, crosses this boundary, the escape velocity required exceeds the speed of light. Because nothing can travel faster than light, everything that crosses the threshold is irrevocably trapped within the region surrounding the singularity, making the black hole fundamentally invisible by direct light emission.