What type of easement exists solely for the benefit of an individual and cannot be transferred?

An easement in gross is a type of easement that benefits a specific individual rather than a piece of land. This means it is personal and cannot be transferred to another person or associated with the sale of land. It typically arises for the benefit of a person or organization, granting them the right to use another's property for a particular purpose, such as utility lines or signage, without being tied to land ownership.

In contrast, other options do not accurately represent the characteristics described in the question. A party wall easement relates to the shared wall between adjoining properties and usually benefits both parties involved. Adverse possession is a legal principle that allows one to claim ownership of land under certain conditions, rather than an easement-like benefit. A license refers to a temporary permission to use someone else's property and is revocable at any time, lacking the permanence or transferability of an easement. Thus, the definition and nature of easement in gross clearly establish it as the correct answer.