Users counted within a FormWork instance can be assigned to roles. A role is a tag with which you can better qualify the user. Through this specification it is possible for instance to get all users who have the qualification of the Administrators, or users of the 'group' Sales or region France etc .. etc ..
A user can of course be tagged several times and belong to 'group' France and Administrators. The tagging system allows you to also represent hierarchical memberships (groups that contain groups, for example: Europe contains the group France) tagging the power-user that belongs to the group Europe is the tag that France Europe ...