Does the xprofile directory in BP plugin

From reading the forum and looking at the xprofile directory in bp plugin --- I am assuming it stands for extended profiles --- is that correct? so these are all the functions related to extended profiles --

Also core -- would contain all of the function hooks and filters -- to control registration and login? I am having a few issues in that when they register -- and then login --- and manually go back to the original domain mapped subsite ---- the original site does not recognize that they are logged in