What Does Back Orifice (BO) Mean?

Back Orifice (BO) is a remote administration system that allows a user to take full control of a computer remotely running the Microsoft Windows operating system (OS) across a TCP/IP connection, either through a simple console or graphical user interface (GUI).

Techopedia Explains Back Orifice (BO)

BO was developed by American hacker Josh Buchbinder, also known as Sir Dystic, to expose the security capabilities of Windows 98.