Black holes are regions in space where the gravitational pull is so strong that nothing, not even light, can escape from them. They are formed when massive stars collapse under their own gravity at the end of their life cycle. The boundary surrounding a black hole is called the event horizon, beyond which nothing can return. There are different types of black holes, including stellar black holes, which form from collapsing stars, and supermassive black holes, which exist at the centers of galaxies. These mysterious objects play a crucial role in the structure and evolution of the universe, influencing the motion of stars and galaxies around them.