Users & Groups
Some sites have many users, some sites only have one - the site owner. Concrete CMS allows you to create as many or as few users as you need in the "Members" section of the site. Additionally, you can create User Groups - this allows you to classify different users. Users in specific groups can get special permissions - for instance, if you want users in a specific group to be able to access a special area of the site, you can set permissions on that area of the site to only be accessible by users of that group. With groups and permissions, the possibilities are endless for how you can configure your site to function.
Groups can also be handy just for organizing users, even without assigning them to different permissions.
For an in-depth look at the Members functionality in concrete5, visit the Members area section of the Editor's Reference.