This is the easiest way to explain. It is a continuous length of interlocking fibers used in the production of fabrics, as well as in crocheting, knitting, embroidery and rope making. This means we can separate wool yarn
into two different categories. Thread used for embroidery or sewing machines, and yarn used for crafts such as knitting or crocheting (often called hairballs) are longer lengths purchased as yarn. Yarns can be made from many different fibers. This includes natural and synthetic fibers.
The most common vegetable fiber is cotton, but you can also use other natural fibers such as bamboo. Besides cotton, synthetic polyester fibers make up the two most commonly used fibers. Animal fibers are also often used. Spinning yarn is made by twisting short fibers together in an S or Z twist to make a single thread. The process of twisting fibers into yarn is called spinning, and was one of the earliest industrialized processes. A spun yarn can contain a single type of fiber, or you can spin various types of fibers together into a blended yarn.
Filament yarn consists of filament fibers that are twisted together or simply grouped together. It can consist of one filament, called monofilament, or it can be made of more than one, in which case it is called multifilament. This can be as few as two or three filament fibers, or even as many as 50 or more. When spinning, your yarn consists of twisted strands of fibers. These are called layers when grouped. The strands are twisted together or twisted in opposite directions to form a thicker wire. Whether it is an S-twist or a Z-twist depends on the final twist.
For those threads that look up and to the left, it will be considered an S-twist, and those that look up and to the right, are z-twist yarns. For a single layer, the final twist will always be the same as the original twist. A staple fiber is a fiber that is considered to have discrete lengths. These are short fibers that are spun into a long, spun yarn. Staple length is a term related to the length of the fiber group. This can vary widely depending on the source of the fiber, so the short fiber length will be an average. Staple length has a big effect on the overall yarn; shorter staple lengths will give fuzzy results, while longer staples will give a smoother end result.