Telnet is a contraction of the two words Telecommunications Network, and is one of the major network protocols used on the Internet. It is one of the earliest network protocols, and one of the only original protocols still in common use on the internet. It was developed in 1969, with the RFC 15, and has evolved over the years to be a robust protocol, although with mounting security concerns it is often foregone in place of the secure SSH protocol.
Unlike the graphical interfaces of the HTTP protocol, which have given us the World Wide Web, telnet is a text-based protocol. The original purpose of telnet was to have an easy interface for terminals to interact with one another, using relatively simple command structures and accessible interfaces. Although still in use, telnet is rarely used by the majority of the internet-browsing public, who instead use HTTP browsers and email clients for the majority of their connections.
In the age before personal computers, anyone who wanted to use a computer generally had to access a terminal that was hooked up to a massive mainframe. Originally, each terminal was hooked up to only one machine, which led to a number of problems. For example, if one person needed to use a number of different machines, each of which specialized in a different task, they would need to physically go to each different terminal to do one job. This could be frustrating if the terminals were located throughout a large building, but was particularly maddening of the mainframe you needed to use was located at an institution in a different city or country from you.
The telnet protocol helped overcome this difficulty. By using a simple suite of commands, users could log in to a distant terminal and ask the mainframe there to undertake whatever processes they needed accomplished. The results would come back to them through telnet, and it was as though they were sitting in front of the terminal itself. In many ways, telnet helped revolutionize the way research was done, and helped build what would eventually become the internet we know today.
Of course, not all of the early uses for telnet were so practical. In fact, one of the ways in which telnet is still used to this day has its roots back in 1978, when a student at Essex University built on the earlier success of terminal games like Adventure and Zork to create a Multi-User Dungeon game, or MUD. These virtual environments, which include other varieties like MUSHes and MOOs, allow multiple people to connect to a terminal via the telnet protocol. Once there, they can play a collective game, often fantasy themed, by inputting text commands and reading the responses and inputs from other players. Although the use of MUDs has diminished with the advent of graphical Massively Multiplayer Online Role-Playing Games (MMORPGs), they still remain a major use of the telnet protocol, with hundreds of thousands of players worldwide.
Although at one point telnet was used widely as a protocol by network administrators and those who needed to deal with their servers, it is rarely used for this purpose anymore. In 1995, a researcher at the Helsinki University of Technology in Finland, fed up with the security holes in telnet which allowed for malicious password sniffing and attacks, built a new protocol to replace it. This protocol, the Secure Shell, or SSH, has most of the same features of telnet, but has much more robust security.