Open Grain vs. Close Grain

Open-grained (also coarse- or ring-porous) woods have large, clearly visible pores across the grain -- oak and ash are the classic examples -- while close-grained (fine-textured, diffuse-porous) woods like maple and cherry have pores small and evenly distributed enough that the surface reads as smooth and uniform even unfinished. The distinction is purely about pore size and visibility, independent of the wood's actual hardness -- some open-grained woods are quite hard, some close-grained woods are relatively soft.

It matters directly for finishing: an open-grained species finished with a standard film finish alone still shows its pore texture faintly through the film, which is why a glass-smooth finish on oak or ash typically calls for a pore-filling step first, packing the open pores level with the surrounding wood before the topcoat goes on -- a step close-grained species like maple or cherry simply don't need.