Wall

A ** wall ** is a usually solid structure that defines and sometimes protects an area. Most commonly, a wall delineates a building, separates space in buildings into rooms, or protects or delineates a space in the open air. There are three principal types of structural walls: building walls, exterior boundary walls, and retaining walls.  Building walls have one main purpose: to support roofs and ceilings. Such walls most often have three or more separate components. In today's construction, a building's wall will usually have the structural elements, insulation, and finish elements, or surface. In addition, the wall may house various types of electrical wiring or plumbing. Electrical outlets are usually mounted in walls. Boundary walls include privacy walls, boundary-marking walls on property, and town walls. These intergrade into fences; the conventional differentiation is that a fence is of minimal thickness and often is open in nature, while a wall is usually more than a nominal thickness and is completely closed, or opaque. More to the point, if an exterior structure is made of wood or wire, it is generally referred to as a fence, while if it is made of masonry , it is considered a wall. Retaining walls are a special type of wall, that may be either external to a building or part of a building, that serves to provide a barrier to the movement of earth, stone or water. The ground surface or water on one side of a retaining wall will be noticeably higher than on the other side. A dike is one type of retaining wall.