This principle prevents any part of the computer system from being under the control of a single person. Every duty or transaction therefore requires multiple people to be involved, with tasks being split among them. In banking, this idea has long been part of the security features of the financial community as a means to control fraud and theft. Now the same concept is applied to computer systems and information security practitioners.
Graham, R. Hacking Lexicon. [Online, 2001.] Robert Graham Website. http://www.linuxsecurity.com/resource_files/documentation/hacking-dict.html.