JIRA administrators have the ability to make changes to the system configuration and schemes, and to manage users. The administrative user is created when JIRA is installed. In big organizations where there is a team of people taking care of JIRA, there could be multiple JIRA administrators. There is a group called jira-adminstators in JIRA. The administrative user that is created during installation is part of this group, and more users can be added to it later on.
Go to Administration | System | Global Permissions (under SECURITY):
If you notice, from the administrative point of view, JIRA offers two different permissions called JIRA System Administrators and JIRA Administrators.
Users who are part of this global permission can perform all the administrative functions. They can make changes in the configuration and scheme, perform system restore, and modify mail configurations as well.