Telnet

Telnet is a common name for a remote login protocol in a communication network. It allows someone at a terminal on one system (usually a time-sharing system) to log into another system (again, usually a time-sharing system) as if they were using a terminal attached directly to the remote system.

It requires two pieces of software: an application (the client) which runs on the system where the user is, and a server (along with the necessary support from the operating system) on the remote computer.

It is almost always part of a protocol suite which includes other protocols which it uses to do its own job, e.g. a reliable byte stream protocol.