- A server, application, or system that serves as an intermediary between a private network, such as a LAN, and all other networks. Its two main functions are to provide document caching and access control. When caching, a proxy first attempts to access data which it has cached, and if not present there, it fetches it from a remote server where said data resides. When controlling access, it serves as a firewall. Also called proxy, or application level gateway.