Exactly what it sounds like. A character deliberately hurting themselves, most commonly by using a sharp blade or claws to cut through the skin in multiple areas, usually to the point of bleeding. This is usually a symptom of a mental illness, but may be part of a ritual.

Usually seen in vent_art as a coping mechanism to actually self-harming in real life. If you find yourself self-harming, it is best to seek professional help.