Bluesky Directory
An AppView is an application in the Atmosphere. It's called an "AppView" because it's just one view of the network. The canonical data lives in data repos which is hosted by PDSes, and that data can be viewed many different ways.
AppViews function a bit like search engines on the Web: they aggregate data from across the Atmosphere to produce their UIs. The difference is that AppViews also communicate with users' PDSes to publish information on their repos, forming the full application model. This communication is established as a part of the OAuth login flow.