What exactly are black holes ?

 In my previous post i explained different types of black holes and how they are formed so now i read some articles and would like to explain what exactly are black holes. We already know that black holes are formed when a star dies causing an explosion. Matter from the star is squeezed into really tiny space causing the gravity to be so strong that that even light cannot escape it's grasp (speed of light is something around 300 000 000 m/s :) ).  Since light cannot escape, it makes black holes invisible. Astronomers find black holes by observing radiation that they emit or look for strange behaviours of nearby stars. When we look at a picture of a black hole we can see two things : singularity and event horizon. Singularity is the center of a black hole where matter is compressed into infinitely tiny point and gravity is very strong. Event horizon is the red part around the center and where everything close to the black hole is being "sucked" inside by the gravity.

source:https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
https://www.space.com/black-holes-event-horizon-explained.html