also known as: 4S, foursquare
Lumber that has been milled flat, square, and parallel on all four sides — the goal of the dimensioning process.
Four-square the stock before laying out joints.
Surfaced four sides. All four faces of the board are dressed, ready for joinery.
The process of bringing rough lumber to final flat, square, sized pieces. Usually face-joint, edge-joint, plane to thickness, rip to width.