A wall is a freestanding vertical plane, or a similar solid or hollow upright structure, which forms a continuous or nearly continuous outdoor barrier. It may form a loop, a polygon, or a line of any shape, and it may be interrupted along its route by gateways or by other structures embedded within the wall.

The barrier can follow a straight, curved, or polygonal route, including a closed loop. Its function does not require a completely uninterrupted surface.

Gateways and structures embedded along the route can interrupt the wall. A solid or hollow upright construction remains distinct from the lighter mesh or sheet arrangement usual for a fence.