- (written as TACACS)Acronym for terminal Access controller Access control system. An authentication protocol in which an access server communicates with an authentication server to determine whether access to a network will be granted. TACACS has mostly been superseded by TACACS+, XTACACS, or RADIUS,
- An enhanced version of TACACS, which includes data encryption and a challenge/response system. Despite its name, TACACS+ is not compatible with TACACS, nor XTACACS.