Self-injury is defined in various ways, but the definition utilized by this website is as follows:
Non‐suicidal self‐injury (NSSI) is the deliberate damage to one’s body tissue in the absence of suicidal intent (NSSI; International Society for the Study of Self‐Injury, 2018). NSSI can include cutting or scratching the skin, although the range of behaviors is diverse (Swannell et al., 2014). Individuals commonly report engaging in NSSI as a means of regulating particularly intense or unwanted emotions (Taylor et al., 2018).*
This definition is important. For one thing, it helps distinguish self-injury from suicide attempts. This distinction has resulted in the term nonsuicidal self-injury (NSSI). The two behaviors are very different and have very different motivations. In short, suicide is an attempt to die, and self-injury is coping mechanism for survival. This definition also helps to differentiate between pathological self-injury and social self-injury such as tattoos and body piercing. It may sometimes be difficult to tell whether or not the behavior is socially motivated, but the student may be able to provide this information. Finally, the self-injury referred to on this website is not that which is often found in cases of intellectual disability, autism, or other developmental disorders- it is self-injury that is done by someone who is fully aware of what they are doing.
* Quoted from: Modeling pathways to non‐suicidal self‐injury: The roles of perfectionism, negative affect, rumination, and attention control- Tonta, et.al