A server —whether a program or device— that centralizes the traffic existing between the Internet and a private network, intermediating in the requests for resources made from the devices of the private network to a public IP address. This way, the public IP server will not know what device made the original request.

This strategic intermediating position enables it to offer different functions: access control, traffic records, restrictions to certain types of traffic, performance improvements, connection anonymity, web caches, etc. On another front, a proxy may provide some security mechanisms (like firewalls), which impede unauthorized access to the private network from outside.

Depending on the context, proxy intermediation may be considered by users, administrators or service providers as legitimate or criminal, so that their use is often debated.