The term 'concrete block' is a building material made of concrete and aggregate, usually sand and gravel. It is formed into blocks of various sizes and shapes and is used in the construction of walls, foundations, and other structures. The crossword solution for this term is 'SLAB, ' which is a flat piece of concrete that is used as a foundation or flooring material. Slabs are often used in the construction of driveways, patios, and walkways.