A future estate with some uncertainity - either in the identity of the possessor ("then to my children" leaves uncertainity as to how many children there will be) or if the person will actually take the estate ("to my son, unless he moves away").
See: Future Interest
Definition from Nolo’s Plain-English Law Dictionary
A future interest in property that will pass only if certain circumstances occur, or that will pass to an unknown person or entity. For example, John makes a will that leaves his farm to Frank for life and then, if Scotty has gone to college by the time Frank dies, to Scotty.
Definition provided by Nolo’s Plain-English Law Dictionary.
August 19, 2010, 5:13 pm