A buttress is an architectural

Architecture

Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...

 structure built against (a counterfort) or projecting from a wall

Wall

A wall is a usually solid structure that defines and sometimes protects an area. Most commonly, a wall delineates a building and supports its superstructure, separates space in buildings into rooms, or protects or delineates a space in the open air...

 which serves to support or reinforce the wall. Buttresses are fairly common on more ancient buildings, as a means of providing support to act against the lateral (sideways) force

Force

In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

s arising out of the roof

Roof

A roof is the covering on the uppermost part of a building. A roof protects the building and its contents from the effects of weather. Structures that require roofs range from a letter box to a cathedral or stadium, dwellings being the most numerous....

 structures that lack adequate bracing.

The word buttress, in a much more general sense, means to support; one might buttress another person's argument, for instance. By visual analogy, that which looks like a buttress may be called so; eg Buttress root

Buttress root

Buttress are large roots on all sides of a big bottomed tree or shallowly rooted tree. Typically, they are found in nutrient-poor rainforest soils and do not penetrate to deeper layers. They prevent the tree from falling over while also gathering more nutrients...

 at the base of the trunk of a tree.

Terminology

In addition to flying and ordinary buttresses, brick and masonry buttresses that support wall corners can be classified according to their ground plan. A clasping or clamped buttress has an L shaped ground plan surrounding the corner, an angled buttress has two buttresses meeting at the corner, a setback buttress is similar to an angled buttress but the buttresses are set back from the corner, and a diagonal (or 'french') buttress is at 45 degrees to the walls.

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