In architecture, an ell is a wing of a building perpendicular (at a right angle) to the length of the main portion (main range).[1]
It takes its name from the shape of the letter L. Ells are often additions to a building. Unless sub-wings or a non-rectangular outline floor plan exists such a wing makes the building L-shaped or T-shaped "in plan" (shape from above/below), though if not central nor at one end of the building the T-shape will be an offset T. Where a building is aligned closely to cardinal compass points, such a wing may be more informatively described by its related side of the building (such as "south wing of the building").