System Administrator
Role that grants users and groups complete control over all permissions, configurations, apps, and administrative options
The term "System Administrator" has two related meanings: the first is technical, the second informal. The technical sense of "System Administrator" refers to the name of a permissions role granted to an individual user or group. Being granted this role means being given control of every Confluence and app administration and configuration option available. In effect, this role creates a Confluence "superuser" who faces no limitation to what she can access.
The second use of "System Administrator" is more colloquial. It simply refers to a user that has, or is a member of a group that has, the above-mentioned permissions role. For example, we might say in our documentation that "only System Administrators can install Brikit." Here we are using this term informally to refer to a user with the role of System Administrator.
There are two important further considerations:
Confluence Administrator is another permissions role (and colloquialism) in Confluence. Like System Administrator, it can be applied to users or groups. The Confluence Administrator does not have full access to the complete set of administrative and configuration options. It is a more limited role than System Administrator.
Please see the Global Permissions Overview page of the Atlassian Confluence documentation for a complete list of the differences between these roles.There is an out-of-the-box Confluence group called confluence-administrators with the System Administrator role assigned to it. This group is, in fact, a set of superusers, and therefore should not be referred to as "Confluence Administrators," despite the group's name. For accuracy, any individual user in this group should be called a "System Administrator." (By contrast, you may create a different group, say, technical-librarians, that has the Confluence Administrator role and whose members could be called, accurately-speaking, "Confluence Administrators.")