There are three different textile spinning crafts (also can be called techniques), namely woolen, semi-worsted and worsted. So naturally there are three kinds of yarns and they are woolen yarn, semi-worsted yarn and worsted yarn. Sometime, people do not know what is called semi-worsted yarn and they do not know the difference between these two types of knitting yarns.

In fact, they come from many times experiments and when comes to spinning techniques, there can be created at least six samples:

Woolen prep plus woolen spun form woolen yarn,

Woolen prep plus worsted spun form semi-worsted yarn,

Semi-worsted prep plus woolen spun form semi-worsted yarn,

Semi-worsted prep plus worsted spun form semi-worsted yarn,

Worsted prep plus woolen spun form semi-worsted yarn,

Worsted prep plus worsted spun form worsted yarn.

Of these, the "worsted prep plus woolen spun" hardest to spin.

Obviously, there is a considerable difference between a worsted-prep, woolen spun and worsted-prep, worsted spun. Taking the exact same fiber source you can end up with six, very different yarns.

What you can learned is that if you have a special fleece, it is well worth the time and effort to try out a variety of techniques to find what will produce the yarn you want. Worsted yarn is the best but semi-worsted yarn is also multivariate for your choices. It's a very exciting step when you go from finding a use for the yarn you made to make the yarn you want.