An event horizon is a boundary in spacetime surrounding a black hole, representing the point of no return. It marks the boundary where the escape velocity required for an object to overcome the gravitational pull exceeds the speed of light. Because nothing with mass or energy can travel faster than the speed of light, anything—including light itself—that crosses this boundary is gravitationally trapped and cannot transmit information or signals back to an external observer. The concept is a defining feature of the region's gravitational warping, suggesting that the physical properties within the horizon are causally disconnected from the exterior universe.