The event horizon marks the boundary beyond which nothing can escape a black hole.

The event horizon is the 'point of no return' around a black hole. It is not a physical surface but a mathematical boundary. Once any matter or light crosses this horizon, it cannot escape the black hole’s gravitational pull. This boundary depends on the black hole’s mass and defines the region where the escape velocity exceeds the speed of light. Observations of stellar motions near suspected black holes and gravitational wave detections support the existence of this boundary.