Self Mutilation is sometimes the term medical practitioners use to describe some forms of body modification, particularly the more "extreme" forms, such as cutting. In the body modification community it is more likely a form of self expression, communication and association with like-minded individuals. It may also be considered a coping tool some may use to help deal with feelings of depression.
Mental health professionals (and sometimes mental health amateurs) typically do not care who wielded the scalpel. A simple, but meaningful scarification piece by a professional body mod artist using sterile scalpels in a clean, ritualistic space tends to be considered "self-mutilation" by mental health professionals. Why? They consider such a cutting to be "self-harm by proxy".
Most people active in body modification find this term offensive.