-Parchment is made from calfskin, sheepskin, or goatskin. The skin would be flayed, soaked (to most of the hair etc.), and then stretched and scraped.
-Vellum is parchment that is specifically made from calfskin.
-A quire is a measurement of paper (or in this case parchment) quantity. In the Middle Ages it usually consisted of 4 folded sheets of parchment, resulting in 8 leaves (16 sides).
-A codex a collection of quires bound together in the form we are now used to for books. Historically speaking, the word “book” (or rather, its Latin/Greek/what-have-you translation) covered groups of scrolls as well as codices.
-A palimpsest is parchment that has been scraped clean of whatever was previously written on it so it could be reused.
Second, a brief history:
Parchment was first developed in either the mid 3rd or early 2nd century BCE in the Greek city of Pergamon as a substitute for papyrus, though the history of writing on animal skins goes back much further. It was widely used in Ancient Greece and Rome, but not so much as its heyday in the Middle Ages in Europe, when papyrus wasn’t an option. Many early Islamic texts were also written on parchment. Paper became available in Europe in the 1200’s and by the late 1400s was more widely used. Parchment is still used today by some traditional Jewish communities as the only acceptable medium for religious texts.
Finally, a few more interesting facts:
-Parchment was expensive. This is why palimpsests became a thing. This is also why people took great care not to waste it.
-A medieval scribe wouldn’t just discard a piece of parchment that had a hole, or a ragged edge. They might not use it for anything of especial value, but it would be used for something. Sometimes holes became part of the artistry of the work. See, for example here and here.**
-Errors could be fixed. Often a scribe could scrape the mistake off and redo that bit. Or, if they had skipped a word or letter, they would just squeeze it in there anyway.
-Parchment is sensitive to changes in humidity and warps easily. This is why medieval codices were so often bound very tightly with wood covers and metal clasps.
*You know, I’ve been wondering if herding sheep would be a valid career choice for a Hogwarts graduate. You really have to wonder where they’re getting all of that parchment. I mean, they could probably produce some of it magically, but I assume you have to start somewhere. I like the idea of herds of magical sheep or some equivalent.
**Or just go read the parchment tag over there. He has some really cool stuff.