Telnet is the early ARPANET protocol that lets a user log in to a remote computer over a network.
Telnet provided interactive remote terminal access: a user’s local keyboard and display could act as though they were connected directly to another host. This made it possible to run programs, inspect files, or use time-sharing services on a distant computer, subject to that host’s permissions and account system.
The protocol emerged during the ARPANET’s early application development. Telnet was developed in 1969, beginning with RFC 15, and was later expanded through additional specifications. It operated as an application-level service above the network’s underlying communication mechanisms, alongside other early ARPANET applications such as FTP for file transfer.
Telnet is often confused with SSH because both support remote login. The crucial difference is security: traditional Telnet sends session data, including credentials, in plaintext, making it vulnerable to interception. SSH, introduced much later, provides encryption and authentication and is the modern choice for secure administration. Finger was mainly a user-information service, while Gopher organized and retrieved networked documents rather than providing general remote login.