A concrete masonry unit (CMU) is a rectangular block made from concrete, often used in construction. These blocks are typically hollow, which makes them lightweight and easier to handle. CMUs are commonly used for building walls, foundations, and other structures due to their strength and durability. CMUs come in various sizes and shapes, allowing for flexibility in design. They can be stacked and bonded together with mortar to create sturdy walls. Additionally, insulation can be added to improve energy efficiency, making CMUs a popular choice in both residential and commercial construction projects.