A concrete masonry unit (CMU) is a standard-size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
Those that use cinders (fly ash or bottom ash) as an aggregate material are called cinder blocks in the United States, breeze blocks (breeze is a synonym of ash) in the United Kingdom, and hollow blocks in the Philippines. In New Zealand and Canada they are known as concrete blocks (a name common in the United States also). In New Zealand, they are also called construction blocks. In Australia, they are known as Besser blocks or Besser bricks, because the Besser Company was a major supplier of machines that made concrete blocks. Clinker blocks use clinker as aggregate.