Superuser is System Manager

Superuser (aka "root") is the UNIX System Manager

On any system someone must be able to kill any runaway program, purge corrupted files, reset passwords when users forget them, remove users' permission to use the system, and a myriad of other system management tasks. On MPE this person is called the System Manager (actually, any user with SM capability).

On UNIX this special user is known as superuser or root (not to be confused with the root directory). Superuser can override file security and do almost anything she wants on the system (she cannot see your password, since it is encrypted, but she can change it). In fact, any user with a userid of 0 is a superuser. Naturally, such users should always have a password.

It is not good practice for the system administrator to always logon as superuser. It is too easy to make a trivial mistake and damage the system, perhaps by rm * in an important directory. Instead, logon as a regular user, then switch to superuser with the su command when you need it.

Root is Also the Start of the Directory

In a Hierarchical File System, one directory is the root or start of the tree. Other directories hang off root and they in turn can have subdirectories. On UNIX and POSIX, root is specified as a forward slash "/". On DOS, root is specified as a backward slash "\". This meaning of root should not be confused with the alternate meaning of root as the UNIX system manager (that is, superuser).