A rough girdle is considered a blemish since it only occurs on the surface of the diamond. Bearding which occurs below the surface may or may not accompany a rough girdle.
A bearded girdle designates small inclusions (below the surface), whereas a rough girdle designates blemishes (on the surface). Generally a stone must have a rough girdle in order to produce the bearding (small feathers protruding into the stone). But bearding doesn’t always occur with a rough girdle, as that relates to the amount of pressure the girdler has put on the stone during the girdling process. The roughness is obvious under magnification, revealing a granular surface that is unattractive.
On lower-cost rough, the polish, symmetry, and finish of the girdle won’t necessarily help the value or salability of a diamond, so cutting speed is the primary goal. The more the shop cutters produce, the more they get paid, and the rougher the girdles get in the process.
An ideal girdle (that isn’t faceted) is smooth and waxy in appearance. Some cutters go a step further by burnishing the girdle into a shiny, smooth surface.