A: Cutting is the act of creating an open wound in ones own skin in order to bleed. It is also known as self-mutilation.
Sometimes people cut themselves because they feel “numb” and want to cut in order to experience some kind of feeling . An example of this can be when someone is feeling apathetic; as though nothing matters and they don't care about anything. Sometimes cutting is a way to “bring them back to reality.”
Other times it is because they have too many emotions, but they don't know how to cope with them. For example, someone who was taught at a young age not to cry because it shows weakness. If something makes this person depressed to the point where they want to cry, instead of crying they might cut themselves. (source here)