S4S & 1S2E Trimboard FJ Pine

S4S refers to Smooth 4 Sides:
It has been planned on all 4 sides and generally has a square edge. As result, it is approximately a 1/4-1/2” smaller in both dimensions than its namesake.

1S2E stands for Smooth 1 Side and 2 Edges:
It will be 11/16” of an inch thin by a 1/2” smaller than its title since it has been planned on the one face and the two edges. It is often referred to as “good one side”