An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of sidewalks, bridges, railway tracks, piping systems, and other structures.

The expansion joint can be as simple as a caulked separation between two sections of the same materials. More recently, expansion joints have been included in the design of, or added to existing, brick exterior veneer walls for similar purposes. In concrete and concrete block ("CMU") construction, the term applied is control joint, but serves a similar purpose.

http://en.wikipedia.org/wiki/Expansion_joints