Yarn

Yarn is a continuous often plied strand composed of either natural or man-made fibers or filaments and used in the production of fabrics and also in crafts, such as weaving, knitting, embroidery, sewing, and crochet to create fabric.

Do not confuse yarn with wool.

Yarn is the oldest and most common textile fiber that is made up of natural protein fibers twisted together into strands. It can be made from natural or synthetic fibers.

Whereas wool is an animal fiber that originates from animals. It is derived mostly from the fleece of sheep. However, there is also wool produced from different animals like goats, rabbits, lambs, etc. 

Wool is the raw material that is spun to make yarn.