Fee simple defeasible is a type of property ownership in which the owner has full and absolute ownership of the property, but with certain limitations or conditions placed on the use of the property. These conditions or limitations can take many forms, but one common example is a reversionary interest, where the property will go back to the grantor (the person who gave the property) if certain conditions are not met, such as failure to pay taxes or use the property for a specific purpose.
One of the most common examples of fee simple defeasible is the fee simple subject to condition subsequent, where the grantor reserves the right to take the property back if certain conditions are not met, and the grantee (the person receiving the property) holds the title with that condition.
This type of ownership is less common than the traditional fee simple ownership and it's mostly used for specific scenarios, for example for properties that are donated for charitable purposes, or for properties that are held in trust.