(sometimes lowercase) Informal.fellow; guy: the average Joe who works for a living.
Informal.a personification of a typical, often unprepossessing representative of an occupation, personality trait, state of being, etc., that is expressed, sometimes metonymically, as a mock surname: Joe Lunchbucket working hard at some factory and paying his taxes year after year; political con artists relying on the gullibility of Joe Schmo.
"coffee," 1941, of unknown origin. Meaning "generic fellow, man" is from 1846, from the pet-form of Joseph (q.v.). Joe college "typical college man" is from 1932. Joe Blow "average fellow" is U.S. military slang, first recorded 1941.