relation back n: the assigning of a prior date (as the date of execution of a document) to an act (as filing of a document and esp. a pleading) as the time of its effect esp. to avoid a time limit [the relation back of amendments to the date of the original pleading]
: the legal fiction that an action (as the filing of a document) was taken on a previous date to avoid the expiration of a time limit
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.