The Guest user (Empower Pro Only) is allowed to bypass normal registration procedures. If Guest access is enabled, there will be a special Guest Button in the registration dialog. It is important that you carefully consider if you want that kind of access, and limit the amount of access you grant the Guest user. You can turn off Guest access in Volume Preferences: Volume Startup.
A second operating system that runs on the user’s primary operating system – e.g., VSE/ESA running as a guest under z/VM.
Anyone who connects to a server without supplying a name. Guest access is set in the File Sharing control panel on the Users & Groups tab, and is turned on or off with Mac OS file sharing.