(1) A term used in grammatical description to characterize pronouns which may be used to introduce a postmodifying clause within a noun phrase, and by extension to the clause as a whole. In classical transformational grammar, the process of forming a relative-clause construction is known as relativization.
(2) A term used in linguistic theory to refer to a type of universal. A relative universal is one which characterizes a general tendency in a language, and allows for exceptions; it contrasts with absolute universal.
(3) A term used in historical linguistics, referring to one way of characterizing the temporal relationship between language changes: to say that one change occurs before another is a statement of relative chronology. A contrast is intended with absolute chronology, where it is possible to state the specific time-periods when the changes took place.