Terminal Access Controller Access Control System (TACACS)
Terminal Access Controller Access-Control System (TACACS) is a remote authentication protocol that is used to communicate
with an authentication server commonly used in UNIX networks. TACACS allows a remote access server to communicate with an authentication server in order to determine if the user has access to the network.
But RADIUS is also remote authentication protocol which is used in WINDOWS, and working between RAS (Remote access server) and IAS (Internet Authentication Server).
Authentication protocol, developed by the DDN community, that provides remote access authentication and related services, such as event logging. User passwords are administered in a central database rather than in individual routers, providing an easily scalable network security solution. It is a protocol use to implement AAA.