Definitions for "Sub Floor"
Keywords:  joist, plywood, osb, laid, sill
sheathed material which is laid directly across the floor joists to form the floor. Can be particle board, but plywood is preferable.
Usually, plywood sheets that are nailed directly to the floor joists and that receive the finish flooring.
Generally referred to as the floor's structural layer. This could be a concrete slab, or a layer of some type of wood or particle board directly attached to the floor joists.