Something which is meant to improve the value or usefulness of a lot can be called an appurtenance to the lot. Structures such as buildings, driveways, pavements, patios or other surfaces, wells, septic systems, signs, and similar improvements which are considered permanently attached to the land in the lot are considered to be real property, usually part of the lot but often parts of a building, such as condominiums, are owned separately. Such structures owned by the lot owner(s), as well as easements which help the lot owners or users, can be considered appurtenances to the lot. A lot without such structures can be called a vacant lot, urban prairie, spare ground, an empty lot, or an unimproved or undeveloped lot.