An easement is a legal right for someone other than the property owner to use part of the property for a specific purpose, such as a utility company running lines, a neighbor sharing a driveway, or a path to a landlocked parcel. It stays attached to the property when it sells, since it is a right in the land rather than a right that belongs to whoever currently owns it.
Why it matters
An easement on your property transfers to the buyer along with everything else, whether or not anyone mentions it during the sale.
General information, not legal or tax advice.