No one wants to read a glossary of terms so we will keep this short but it's important to know what we are talking about when we use a term or abbreviation.
AdminCP/ACP = Administration Control Panel which is the backend control area of your Suite
Member = Any user account in the system
Member Group = Control permissions and settings for members assigned to that group. All members are part of one or more member groups.
Guest = Someone who is browsing your community but is not logged in
Admin = A member who is in a group or otherwise has permission to access the AdminCP
Moderator = A member who has permission to perform any sort of control over other member's posts on the front end
Permissions = Throught the Suite you will see permission options and be presented with a huge selection of checkboxes:
These permission checkboxes define what each member group can see or do within the area of the Suite you are working with at the time. The columns define the various options.