Root

root generally refers to either the "super user" - the user account which has ultimate power over the entire system - or to root privilege, which is the ultimate power itself.

Unlike the Windows environment, under BSD (and typically under other unixlike operating systems as well) the system administrator has the final say on absolutely everything that goes on under the hood. There are many processes and functions that the various Windows operating systems deny access to or hide from even administrator-privileged accounts, whereas under FreeBSD there is very literally nothing that system processes are privileged to do but the root user is not.

On older BSD and SysV systems, the root account was actually called "avatar".