This document defines various terminologies related to mental illness including: - Delusions which are firmly held beliefs not shared by others such as beliefs of being spied on or poisoned. Different types of delusions are described. - Hallucinations which are imaginary sensory perceptions that seem real without external stimuli such as seeing or hearing things that are not present. - Other terms defined include agitation, phobias, dementia, depression, mania, as well as types of thought disorders. Insight is also described as understanding of one's own illness.