term:

Vulgar Substitution

vulgar substitution n

[French substitution vulgaire, from Latin substitutio vulgaris, literally, ordinary substitution, as distinguished from substitutio pupillaris substitution of an heir in place of a minor who actually receives the testamentary gift but dies before reaching the age of majority]
in the civil law of Louisiana
: a testamentary disposition in which the person making the will names another person to take the gift in the event that the instituted heir does not accept it or is already deceased

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.