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.