Jef is a short form of the name Joseph, which is of Hebrew origin and means "God shall increase". The name Joseph has been popular for centuries due to its biblical association with Joseph, the husband of Mary and father of Jesus in Christianity.
The name Jef itself began to gain popularity in the late 19th century as a diminutive form of Joseph. It was particularly common in Belgium and the Netherlands, where it continues to be used today. In France, Jef is also associated with Belgian singer Jacques Brel, who often went by the nickname Jef.
In terms of famous people named Jef, one notable example is Belgian footballer Jef Mermans, who played as a striker for clubs such as RSC Anderlecht and Standard Liège in the mid-20th century.
"The name Jef was quite popular in the late 1950s and early 1960s, with a peak of 15 births in 1963."