They are the thick steel area between the sharpened edge and the handles. Bolsters provide additional rigidity, weight, safety and improved balance to a knife. The best kitchen knives are flat ground. The blade profile tapers from the thicker spine to the thinner edge in a straight or convex line. They are heavier and tougher than hollow ground blades which have a concave profile.
Serrations are the wavy type of blade edges.
We consider this an outstanding feature on bread knives and recommend that your bread knives have it. As long as you keep your edges sharp, plain edges are better for other kitchen purposes. A well sharpened plain edge knife should slice a ripe tomato cleanly and easily. Serrations are popular in lower priced knives because they will cut better when dull than a plain edge blade. We recommend plain edge blades for people who can and will keep their edges sharp.