The Administrator is a user account typically found on Microsoft Windows platforms based on Windows NT, including desktop operating systems Windows 2000, XP and Vista and the server platforms NT 4.0 Server, Windows Server 2000 and Windows 2003 Server (and variants). It is the "super-user" account typically used by IT systems personnel to maintain these operating systems.
On FreeBSD and other UNIX and Unix-alike platforms (including Linux) the equivalent to the Administrator account is the root account. This is the "super-user" of Unix and is similarly used by IT systems personnel.
The two super-user accounts are similar in that they exist as part of the default installation and give top-level access to the operating system.
On Microsoft platforms regular user accounts can be given Administrator privileges where-as on Unix platforms a regular user must be given rights to issue the su command to gain a root shell, or rights to use sudo to execute a specific command or script as root.
There are absolutely no system processes more privileged than root and there is no restriction on what root can do on a FreeBSD system. If you type rm -rf /* as root, all files on your system (including system files) will be deleted without even asking for confirmation. (Don't do this on a system you weren't about to format anyway!)
Remember: "With great power comes great responsibility."