Okie is an informal term for someone from Oklahoma, and is often used as a nickname for Sooners, the nickname of the University of Oklahoma's athletic teams. The term 'SOONER' is derived from the settlers who illegally entered the Unassigned Lands in the Oklahoma Territory before the official opening date of April 22, 1889. Thus, the term 'Okie' is an informal way of referring to someone from Oklahoma, and is often used as a nickname for Sooners.