term:

Life In Being

life in being

:the life of a particular person (as a lineal descendant) in existence at the time of the creation of a deed or will or at the time of the testator's death [the interest must vest by the end of lives in being plus 21 years] see also rule against perpetuities

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