Which term describes the legal right of a property owner to use part of someone else's property for a specific purpose?

The term that describes the legal right of a property owner to use part of someone else's property for a specific purpose is easement in gross. An easement in gross provides an individual or entity the right to use the land of another solely for a specified purpose, such as utilities, transportation, or access, without necessarily having any ownership interest in the land itself. This form of easement is particularly relevant for cases where the use is for the benefit of an individual rather than for a parcel of land, making it distinct from other easements, which typically benefit a specific piece of land.

In contrast, a fee simple estate refers to the most complete form of property ownership, encompassing full rights to the land and its usage without limitations. Conveyance is the act of transferring property from one party to another, focusing on the movement of ownership rather than the rights to use someone else's property. Adverse possession is a legal doctrine that allows a person to claim ownership of land under certain conditions, effectively taking possession of someone else's property over a period, which does not relate to the allowance of use for specific purposes.