Heartwood & sapwood
Heartwood is the older, harder and more central portion of the tree. It contains deposits that contribute to a darker look and feel. Because heartwood is denser and less permeable, it's more durable.
Sapwood is the softer, younger, middle portion of a tree between the heartwood and the new growth under the bark. Sapwood is typically permeable, less durable and lighter in color than heartwood.
Heartwood and sapwood take stains and finishes differently, influencing the ultimate appearance of the floor. Heartwood is more dimensionally stable than sapwood, so a floor with a higher concentration of heartwood will tend to shrink and swell less than flooring that is mostly sapwood.
Wood grain & texture
"Grain" and "texture" describe similar attributes. Grain often describes the growth rings of wood - coarse for larger rings and fine for closer and tighter annual rings. Grain is also used to indicate the direction of the fibers, whether straight or swirling. Grains are said to be open or closed depending how open the pores are. It matters because it affects the way the wood accepts stains and finishes.
"Texture" usually describes the finer aspects of the wood, and may be more subjective than objective.
