PuTTY is a free and open source terminal emulator application developed by Simon Tatham. It’s the most popular terminal emulator on the internet supporting protocols such as SSH, Telnet, SCP, SFTP, serial, rlogin, and raw socket. Given its open source nature, there are forked versions of PuTTY that provide additional features and functionality.
The most common usage of PuTTY is for terminal emulation using the SSH or Telnet protocols. These protocols allow remote terminal access for administration of servers or devices running SSH or Telnet servers.