A Member is someone who’s registered to your service, but not necessarily logged into the application/site.
A Guest is someone who uses your services without being registered or logged in.
User is too broad of a term, in my opinion. A user can be anyone, whether he or she is a member or guest. Basically, anyone who uses the application.
Authenticated User or Authenticated Member is closest to what I’m searching for, but I’m still holding out for a shorter term.