Fee-simple-determinable definition

(law) A defeasible fee created with clear durational language expressing a condition (e.g. "so long as", "until", "while") which causes ownership of a property to revert to the grantor upon the occurrence of that condition.

Joe gives Mike an estate in land "so long as no alcohol is brought onto the property"; this creates a fee simple determinable - if alcohol is brought onto the property, ownership of the land automatically reverts to Joe.