RADIUS stands for Remote Authentication Dial-In User Service. RADIUS is a system used by many Internet Service Providers (ISPs) to provide authentication and accounting. For example: when you dial in to the ISP you are prompted for a username and password. This information is then passed to a RADIUS server, which checks that the information is correct, and authorizes access to the ISP system.
Meaning of RADIUS in English
DAX English glossary of key connectivity terms. Английский глоссарий основных терминов по коммуникациям DAX. 2012