New Followers: New Vocabulary
Ply- yarn is made by spinning your fiber (wool, alpaca, silk, buffalo fur, pet fur, camel fur, etc) into thin strands. Those first thin strands are plies. Then you spin those together, two at a time, then spin the two-ply strands with other ones and so on, until the yarn is as thick as you want it.
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I wanted to point out that this is not actually true. Singles (another name for what comes off the spinning wheel) can and usually are combined in any number from 2 to a very large number (twelve or more). Two-ply yarn is very common from handspinners, but commercial yarns tend to be three- or four-ply, or even more. Three and four ply yarns are rounder than two-ply; two-ply tends to be grabby, which is why it (and its cabled cousins) are most commonly seen in commercial laceweight. Most of the time, plies are combined in one step; a four-ply yarn will have four singles combined in one go. If they are combined in more than one step, the yarn is usually called cabled, and it looks different from regular four-ply.
It used to be true that commercial spinning machines could only spin one thickness of ply/singles, and so they were combined sort of like you describe. However, technology has advanced, and this never was true for handspinners. These days, you can buy bulky weight singles yarn (one ply) and I personally own some cabled twelve-ply laceweight. However, this is why some countries use the ply system for yarn weights (so why bulky might be called a 10-ply or 12-ply, for example). This has nothing to do with the number of plies that are actually in the yarn; it’s a historical hold-over.
