CUFF: The leather band that wraps around and touches your wrist.
STRAPS: Referred to on watch bands and watches. The straps are what actually connect to the watch face itself. The straps are on top of the "cuff".
STRESSED: Used when referring to colors. "Brown Stressed" for example, means that the leather is dyed brown and that it has blackened edges and more of a burnt faded or aged look.
TOOLED or TOOLING: Used to refer to work embossed or performed onto the leather itself. For example, some of the Apple Watch Bands have 'tooling' in the center of them that is sort of a textured look that is embossed into the leather.
WATCH DIAMETER: The distance across the watch face itself, from edge to edge of the case, not including the ears. See this page for a graphic example.
WATCH OPENING: The distance between the ears of the watch face. This is basically the strap size. See this page for a graphic example.