Link to wiki
Black holes are a place in space time where its gravity is so strong that nothing not even light can escape. It is black as it sucks in the surrounding light. It is formed when massive stars die. It can continue to grow by absorbing matter around it. A black hole is very common in the center of most galaxies. Black holes can be detected in many ways such as its interaction with other matter and with electromagnetic radiation.
In my opinion, black holes sounds really scary. I think that any matter that get sucked into the black hole will get ripped into individual atoms. I also believe that the Sun may change into a black hole at the end of its life cycle.