Reversion

A reversion is a property interest retained by an owner when he conveys less than an absolute interest in the property. A reversion is established automatically by law based on a condition of use or termination of an interest by someone else.

For example, a donation of a field to a town so long as it is used for Little League creates a reversion by operation of law if the specified use ceases.

Reversions are not subject to the Rule Against Perpetuities because they are vested interests.