The term 'customary function' can be defined as a ROLE or task that is traditionally performed in a certain way. It is often associated with a specific job or profession, and is usually done in the same manner each time. For example, a doctor's customary function would be to diagnose and treat patients, while a teacher's customary function would be to educate students. Customary functions are often seen as an important part of a job or profession, as they help to ensure consistency and quality of work.