PWE stands for Plain White Envelope.
It’s an abbreviation that is used often within the card collecting community on Twitter, Facebook, IG, etc., when referencing how a trading card will be shipped. The cards will be shipped to you in a standard white letter envelope with minimal protection and NO tracking number. (The exception is the eBay Standard Envelope (ESE) which is a letter mail format devised by eBay in partnership with USPS which provides a non-standard tracking number usable within the eBay website to track your order.)
The alternative to PWE is called BMWT (Bubble Mailer With Tracking).
