concrete block

A Concrete masonry unit (CMU) [US], concrete block, cement block, breeze block [UK], cinder block or foundation block [US], or clinker block (if bottom ash or clinker is used as an aggregate) is a large rectangular brick used in construction. Concrete blocks are made from cast concrete, i.e. portland cement and aggregate, usually sand and fine gravel in the case of blocks. They are formed typically in the shape of two squares joined on one side to form a rectangle, with the insides of the squares hollow. This allows structures to be built in the traditional masonry style of overlapping rows, with the structure's weight carried by the "walls" of the blocks.
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