An administrator account is a login ID on a system with elevated privileges, suitable for managing the system -- installing software, applying patches, managing users, starting and stopping services, etc.
On the Windows operating system, the built-in administrator account is literally called "Administrator." Other common names for built-in administrator IDs include "root" on Unix and Linux systems and "sa" (short for system administrator") on SQL Server databases. There is no need for administrator accounts to have default names and in many organizations it is common practice to rename the built-in administrator account to have a different name, so as to make it more difficult to attack them via password guessing and other similar attack methods.
Hitachi ID Privileged Access Manager secures privileged accounts on an enterprise scale: