A paver base is made up of three levels: subgrade, subbase, and base. Each layer serves as a specific type of support and has a unique material composition. The lowest layer of compacted dirt beneath the installation site is called a subgrade. "Sub-base" is the term used to describe the intermediate support layer that sits on top of subgrade soil. https://modutile.com/product/gravel-pavers-outdoor-basketball-court-base-24x24/