A good piece of kiln-seasoned wood is stable, defect-free, properly dry for its use, and not over-stressed by aggressive drying. If buying, look for a moisture meter reading consistent with your local equilibrium moisture content and no visible drying defects.
You’re referring to (kiln drying) of wood. A “good piece” of kiln-dried wood generally means one that has been dried carefully, without defects, to the right moisture content for its intended use.