Backdoor

A backdoor into an information system s a method of bypassing normal user identification and authentication while securing access to that system. Often a computer programmer will install a backdoor into a software application or component so that (s) he can gain access into the system without the system recording who (s) he is. A backdoor can be created without modifying the source code of a program by rewriting the complier so that it recognizes code during compilation that triggers inclusion of a backdoor.

Source: FEMA
TEEX