I will be continually adding more information to this section, as different breeds of wool appear in the store or questions about technique and terminology pop up. If you would like me to cover something specific I would be happy to add a segment to this page. Just drop me a line  from the Contact menu!

Commercial/Millspun - Commercially Spun Yarn and millspun are terms that I will use interchangeably on this site because the commercially spun yarn that I have sourced, happens to be all millspun. These terms refer to yarn that was produced by an automated device rather than by hand. Generally "Commercially Spun Yarn" refers to yarn that was produced on a large scale for a wholesale market. "Millspun" usually refers to a smaller operation and the yarn produced could all be for one person/buyer. There are a couple of mills in Alberta that will process fleece for farmers to produce yarn.

Fulling - Fulling is a way of processing fibre (in this case yarn) by applying an abrupt force in order to shock the individual fibres within the yarn. This causes some of the twist energy trapped in the fibre to transfer and equalize along the entire strand and usually results in a bit of fluffing or plumping in the finished product. Fulling a single (yarn that is only 1 ply) helps to stabilize some of the twist so that there is less bias in the finished knit, crocheted, or woven work. It is not necessary to full yarns that are balanced--the twist within individual plies counters the twist applied when they are plied together--however fulling balanced yarns does restore some of the bounce and elasticity that the spinning process may have pressed out.

Merino - Originally a Spanish breed the Merino have been exported across the world with pockets of specialized populations in Australia and North America popping up after breeding shifted from meat to fleece production. Merinos have record breaking fleece when it comes to fineness. Their fibre can span from 24 down to 11 microns (and sometimes even finer)! It is often cross-breed with other breeds to create fibre with unique combinations of staple length and crimp.

Peruvian - This wool is produced by a breed of Corriedale crossed with Merino sheep. The fibres are long and soft. I usually spin this fibre worsted style, but the finished yarn still has a bit of squish and fluffiness to it.

Polwarth - Another breed with merino heritage. It heralds from Australia, with wool that has a long staple length and typically features a micron count between 22-25. I find it soft and fluffy even when I don't full the yarn.

Woolen vs. Worsted - These words describe two different styles of spinning and their product. Usually with terms like "Long Draw" or "Short Forward Draw" techniques associated with them. It's a very handy way of describing yarn and fibre, and you will see me write up descriptions like "semi-woolen" or "worsted spun". It's also good to keep in mind that there is a spectrum between woolen and worsted. You can spin both styles of yarn with either long or short draw (a bit trickier, but still very possible and with great results).   
Woolen usually describes a yarn that was spun with a long draw and with fibres that have been carded, (or combed and folded) and are all slightly misaligned or criss-crossing. Because of the random alignment of fibres, lot's of air and cushion space forms within the strand. The resulting yarn is squishy, and less dense than it would have been if spun worsted style. The finished yarn will also tend to have a bit of a halo around it, or appear less smooth, however that does not mean it's less soft! "Semi-worsted" describes a yarn that is spun with mostly misaligned fibre, or with completely misaligned fibre but with the air pinched out and extra twist applied while spinning to make it more dense and strong.
Worsted usually describes yarn that was spun with aligned fibres that have been combed. Less air is trapped within the strand because all of the fibres stack neatly against each other when twisted. Worsted yarn is more dense which is helpful for draping, and tends to be stronger with tugged on than woolen yarn. It has a smoother appearance and texture. "Semi-woolen" describes yarn that is spun with mostly aligned fibre with a certain percentage of the mix being misaligned to help add fluffiness. 
I have seen, woolen, worsted, semi-woolen/worsted, long/short/forward/inchworm draw all used with slightly different definitions and contexts so always check to see if there is a glossary on the website or book you're reading to make sure your understanding aligns with the writer's intent.

Worsted vs. Worsted vs Worsted - The term worsted can describe the weight of a yarn in the same manner that you would use wraps per inch, the style of spinning yarn, or the fibre alignment qualities of a spun yarn.
See: Yarn Weight or Woolen vs Worsted respectively for more information.