Which term describes ownership that can be defined as permanent except under certain conditions?

The term that describes ownership which can be defined as permanent except under certain conditions is a defeasible estate. This type of estate is characterized by the fact that the owner's rights can be terminated if specific conditions or events occur. A defeasible estate can provide the owner with a title that is seemingly permanent, but these conditions—such as the breach of a covenant or failure to fulfill a condition—can lead to the property reverting back to the grantor or another party.

In contrast, a life estate grants ownership for the duration of a person's life, after which the property passes to another party, and therefore does not provide permanent ownership as it is contingent on the life of the individual. A fee simple estate represents the highest form of property ownership, where the owner has full control without any conditions, making it permanent unless sold or transferred. Remainder interest refers to the future interests that might come into play after a particular estate ends, but it does not itself indicate any condition affecting the permanence of ownership.