Block, in masonry, refers to a large, rectangular building unit that is made from materials such as concrete, stone, or clay. These blocks are typically larger than bricks and are used in construction for building walls, foundations, and other structural elements.

There are various types of masonry blocks, including:

1. Concrete Masonry Unit (CMU): The most common type of block, made from concrete and often referred to simply as "concrete block" or "cinder block." CMUs come in different sizes and configurations, such as hollow or solid blocks.
2. Aerated Autoclaved Concrete (AAC) Block: A lightweight, precast block made from a mixture of cement, lime, sand, and aluminum powder. AAC blocks have good thermal insulation properties.
3. Stone Block: Blocks cut from natural stone, like limestone, granite, or sandstone. These are used in more specialized or decorative masonry work.
4. Clay Block: Similar to traditional bricks but larger, these are made from natural clay and used in load-bearing walls and other structures.

Blocks are laid in courses (rows) and bonded together with mortar to create a strong, stable structure. The size and type of block used will depend on the specific requirements of the construction project.