Concrete blocks can be classified into two main types hollow and solid. These two varieties of concrete blocks can be utilised for a variety of tasks in addition to wall construction.
As you\’ll see, not every solid concrete blocks are completely solid, but they are more solid than hollow concrete blocks. Below, we\’ll go into more detail about the many varieties of concrete blocks, often called as CMU or concrete masonry units.
Source: https://coneccconcrete.com/blog/Types-Of-Concrete-Blocks