The possibility of reverter is a future interest held by a grantor or transferor of property as a fee simple determinable (See possessory estate). Distinct from a fee simple absolute, a fee simple determinable is an estate that has a provision that automatically reverts the property to the grantor if an event happens. The event (or nonevent) that triggers the automatic transfer of property back to the grantor is called the condition subsequent. Thus, the possibility of reverter is the interest held by the grantor that may or may not be triggered and leads to automatic restoration of ownership in the grantor/transferror. This is also distinct from the right of entry, which is a future interest held by the grantor that allows, but does not require, the grantor to restore ownership (See fee simple subject to condition subsequent).
For example, Blackacre grants “the property to A and her heirs so long as the property is used for educational purposes.” After granting this fee simple determinable, Blackacre maintains a possibility of reverter in the property. If A uses the property for a purpose other than education, the property reverts to grantor Blackacre.