What is an Administrator on the Computer?
Administrator (or admin) can have various meanings:
1: someone who manager a computer, which means they have authority to create new users on the operating system, install any software, etc. When you install an operating system, you always have to create at least one user that has this role. On Windows, it's called an administrator. On Linux, a sudoer.
2: someone who manages an online community. In general, you have 3 tiers of users in a forum: the administrator with full powers over the whole website, moderators granted moderating powers by the administrator, and common members. The administrator title typically means they're part of the staff running the website, while a moderator may be an unpaid volunteer.