What is wool?

Any type of certain fiber, such as cotton or flax, prepared after a special process. Also, a sheep/lamb/goat's hair.

I would say that the word "wool" refers to fiber made from sheep's fleece (or hair).

Other animals fur can be used to make yarns, but then they most often would be referred to in different words.
For example:
  • mohair is from the angora goat
  • alpaca is from the alpaca
  • angora is from a rabbit
  • cashmere is from the cashmere goat
  • givuit comes from the artic musk ox
  • camel is from a camel

In addition to yarns made from animal hair/fiber/pelts/fleeces, there are Vegetable fibers: cotton, linen, hemp, bamboo, to name a few.

There would also be manmade yarns, such as: acrylic, nylon, polyester, and spandex.

Yarns that wouldn't easily be categorized in the above manner, would include silk, and a newly manufactured yarn made from soybeans (soy milk), and milk! Yes, I said milk--the best description of the process is like when you make cotton candy, when you put the cone into the spinning cotton candy and roll it around to get the candy on the cone.