What do EUC, GUC, VGC, and Others on eBay, Craigslist, and Elsewhere Mean?

There are a dizzying array of abbreviations on sites on which you can purchase used clothing and other used goods, such as eBay, Craigslist, and Poshmark, just to name a few. Abbreviations such as EUC, VGUC, GUC, EU, NIB and NIP can be confusing, while other abbreviations are more readily recognized, such as NWT and OEM. Here is a guide to all of those abbreviations, be they on eBay, Craigslist, thredUP, Swap, or wherever you may see them.