Think of it like this. The rings( curved lines on the end of the board ) each represent a growing season. At one point, each one of those would be the layer of the tree directly under the bark, with a new ring added every year. The Rays (Medlulary,I don't know if I spelled this right) which are more pronounced on some woods than others,run from the center of the tree to the outside like the spokes of a wheel.Because a tree is tapered ,large at the bottom and smaller at the top, the resulting saw log is not a cylinder.We like our building material to be straight and square ,so we cut the rounded outer sections of the log off, not parallel to the outer surface ,but in straight lines roughly parallel to the axis or centerline of the log (Ideal world). The lumber is then cut off of the sides of this squared timber,to maximise yield. The out sides (slabs) are considered waste and are either sold for firewood ,chipped,or used for fuel to fire the kilns ,heat the mill, or run steam generators, depending on the size and efficiency of the operation. The slabs are what would be ideal for bowyers if you have a small local mill or know someone that runs a portable bandsaw mill, that doesn't use a "debarker". So the "grain" is the growthrings that run the length of the board . The "Endgrain" is the growthrings you see on the end of the board. The "Edgegrain" is what you see on the narrow side of the board. And the "Facegrain " is on the wide side of the board. A board cut with it's endgrain "rings " going from narrow edge to narrow edge , roughly parallel to the wide edge, is called plainsawn. If the growthrings run from wide face to wide face ,it is radial sawn .I know most of you are going to say "Quarter Sawn " but just wait for it!................ If the grain runs on an angle of about 45deg. more or less , it's quarter sawn .Those spokes (rays) we talked about earlier will show up as light coloured streak across the face of the "Quarter" and"Radial" sawn boards. True" Quarter Sawn" and "Radial Sawn" boards will make better bows because of the way they are milled. The Log is cut into "Quarters " and the boards are then cut off of the flat faces Which are parallel to the axis. "Radial " is the first couple of cuts they get from those quarters, as they will have the grain oriented 90deg. to the face. There is also flat cutting ( Mostly specialty for the cabinet and furniture industry)where they just make consecutive cuts through the log ,without taking off slabs or turning the log. Even quarter sawing is very rare in the grand scheme of things. the boards you are getting from the lumber yard are all plain sawn. In each log you will get some boards that have Quarter or Radial looking grain, but it's not necessarily going to be true to the grain of the tree. For the most part , they will suit our purpose ,as long as the grain doesn't run off too much. Let that soak in for a while then we can talk about Knots, Crooks, Twists, Crotches, Figure, Timberbind,Blue stain vs mineral stain,Shakes, Honeycomb...................................................