A term used to describe behaviour that is a result of the interaction between individual and environmental factors, and includes stereotypic behaviour (such as rocking or hand flapping), anger, aggression, self-injury, and disruptive or destructive behaviour. Such behaviour is seen as challenging when it affects the person's or other people's quality of life and or jeopardises their safety.

Behaviour of such an intensity, frequency or duration that the physical safety of the person, or others around them, is likely to be placed in serious jeopardy. It also includes behaviour that is likely to severely limit or deny access to and use of ordinary community facilities.