What does an owner own if the duration of his or her rights in an estate cannot be determined?

The owner own the freehold estate if his or her rights in an estate cannot be determined

Explanation:

In this type the owner will not know the duration for which he or she can hold the estate and they can enjoy exclusively all the rights for an undefined length of time or period

They are of three kinds a fee simple, a fee tail, and a life estate in these type the owner can enjoy the rights for an amount of time that is not known to him and this also includes the ownership in the properties