BP Required Field Notification is a BuddyPress plugin that prevents members from accessing the site until they have filled in any required fields within their profile.
Within BuddyPress, the Xprofile is the Extended Profile, information from which is what you can see when you view the Members>>Username>>Profile page. It is Xprofile fields that are completed when a member signs up for example. The registration page gathers data for the Xprofile “Base” Field Group. Other Field Groups can be added by Admin which are not set up on registration but will also be displayed on the members profile.