What is a Sub-base?

Definition: What Does the Term “Sub-base” Mean?
The term sub-base is used on a construction site to identify a number of situations that have a base below a final surface. The sub-base of a slab on grade, could be a layer of 6″ of stone, the sub-base under a roadway, could be a layer of mixed gravel. Any area, below a finished surface, could be called a sub-base.