This is URL scheme an app needs to add to their info.plist in order to integrate the Facebook SDK. The number after fb is the ID of their page/app on Facebook.
In particular, I think it's used for switching apps - your app switches over to the facebook app (if installed) using fb:// perhaps, and if the user logs in and approves the fb-app, the facebook app will ask iOS to open "fbYOURNUMBER://", bouncing the user back to the app.
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This is URL scheme an app needs to add to their info.plist in order to integrate the Facebook SDK. The number after fb is the ID of their page/app on Facebook.
In particular, I think it's used for switching apps - your app switches over to the facebook app (if installed) using fb:// perhaps, and if the user logs in and approves the fb-app, the facebook app will ask iOS to open "fbYOURNUMBER://", bouncing the user back to the app.