A PR is a Pull Request. It's a way for developers to take changes to code they make and merge it into the main code of an app.
The request allows a maintainer like nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z to review and request changes and provide other feedback before adding features and other improvements.