The species of lumber. The grade itself. The moisture content of the wood at the mill when the stamp is applied . Of all the aspects of the grade stamp, this may be the most confusing to consumers. When a log is sawed into lumber, the wood contains very large amounts of water.
Wood is much like a sponge in that regard.
If we wring the sponge out, the sponge is relatively dry. You wring the water out of the wood by drying the wood. Multiply this by 100 and you have the moisture content expressed as a percent. The oven-dry condition is 0 percent moisture content. Typically, freshly cut logs have moisture contents of 80 to 150 percent, depending on the species of wood.