Self-harm (SH) or deliberate self-harm (DSH) includes self-injury (SI) and self-poisoning and is defined as the intentional, direct injuring of body tissue most often done without suicidal intentions. These terms are used in the more recent literature in an attempt to reach a more neutral terminology. The older literature, especially that which predates the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), almost exclusively refers to self-mutilation. The term self-harm means the same as self-injury.

The most common form of self-harm is skin-cutting but self-harm also covers a wide range of behaviors including, but not limited to, burning, scratching, banging or hitting body parts, interfering with wound healing (dermatillomania), hair-pulling (trichotillomania) and the ingestion of toxic substances or objects. Behaviours associated with substance abuse and eating disorders are usually not considered self-harm because the resulting tissue damage is ordinarily an unintentional side effect. However, the boundaries are not always clearly defined and in some cases behaviours that usually fall outside the boundaries of self-harm may indeed represent self-harm if performed with explicit intent to cause tissue damage. Although suicide is not the intention of self-harm, the relationship between self-harm and suicide is complex, as self-harming behaviour may be potentially life-threatening. There is also an increased risk of suicide in individuals who self-harm to the extent that self-harm is found in 40–60% of suicides. However, generalising self-harmers to be suicidal is, in the majority of cases, inaccurate.