When you spin worsted yarn you need to process the fibers. Assuming we have gone through the carding process, the carded wool can undergo the gilled/heckling stage, then the combing stage, next they are oiled and finally spun. The fibers that make up the strand at the end of the card are not rigorously aligned; some are still tangled: so they are similar to felt. Before combing, it must be scoured, i.e. regularize it, parallelize it and straighten the fibers, worsted yarn is not fulled.
The main purpose of combing is to remove the very short fibers, and the last small impurities that still remain. To do this, the strands are passed through a succession of increasingly fine combs. Like carding, combing provides a raw material for spinning. The amount of wool that is the by-product of combed wool varies according to the qualities (but it is common that between 5 and 12%).
Semi-combed wool is analogous to combed wool, namely: spinning preparation, spinning, coiling and twisting. But it is distinguished by its less fine finish. It is prone to problems and is seen as a less durable. This semi-combed wool is used especially for carpets and blankets.
The "cashmere" under worsted wool is a rather light woolen twill fabric, called serge which is used for military uniforms, suits, and trenchcoats. French serge is softer and often used as jacket linings.