A paver base is comprised of three levels: subgrade, subbase, and base. Each layer provides a specific type of support and has a unique material composition. Subgrade is the lowest layer of compacted dirt beneath the installation site. The phrase "sub-base" refers to an intermediate support layer that sits on top of subgrade soil. https://modutile.com/product/gravel-pavers-outdoor-basketball-court-base-24x24/