ref.

Abbreviation of reference. [(literary or archaic) A relationship or relation (to something).]

(law) Abbreviation of referee (title). [(sports) An umpire or judge; an official who makes sure the rules are followed during a game.]

(law) Abbreviation of refining. [Refinement (process of refining)]

(Christianity) Abbreviation of Reformed. [Of the Protestant movement typically associated with John Calvin, as separated from the Lutheran Church to pursue more extensive reformation.]