Questions about what sort of questions are appropriate for PPCG.
As with pretty much any website that allows user submissions, some questions and answers have appropriate subject matter (are "on-topic") for the site, and some are "off-topic" and closed/deleted as such. On Stack Exchange, topicality for answers is fairly easy to define (an answer is on-topic if it answers or attempts to answer the question given, although it might still be deleted for other reasons). Topicality for questions, however, can be less obvious
The scope tag is for questions on Meta that discuss what sort of topics are appropriate for questions on the main PPCG site; although PPCG has an official definition of topicality, it's often necessary to ask a question on Meta about where exactly the boundary lies, and this tag serves to categorise those questions. The tag can also be used on proposals to change the definition of topicality.