A shelf is a flat, horizontal plane used for items that are displayed or stored in a home, business, store, or elsewhere. It is raised off the floor and often anchored to a wall, supported on its shorter length sides by brackets, or otherwise anchored to cabinetry by brackets, dowels, screws, or nails. It can also be held up by columns or pillars. A shelf is also known as a counter, ledge, mantel, or rack. It can be attached to a wall or other vertical surface, be suspended from a ceiling, be a part of a free-standing frame unit, or it can be part of a piece of furniture such as a cabinet, bookcase, entertainment center, headboard, and so on. Usually, two to six shelves make up a unit, each shelf being attached perpendicularly to the vertical or diagonal supports and positioned parallel one above the other. Free-standing shelves can be accessible from either one or both longer length sides. A shelf with hidden internal brackets is termed a floating shelf. A shelf or case designed to hold books is a bookshelf