LINEMODE SLC (Special Line Characters) is a feature of the Telnet protocol that allows clients and servers to negotiate how special characters - such as backspace, interrupt, or end-of-file - are handled. Instead of sending every keystroke to the server, the LINEMODE option enables the client to process and edit input locally, only sending complete lines or special character actions to the server. SLC negotiation ensures both sides agree on which characters are recognized as special and how they should be managed, improving efficiency and user experience during remote terminal sessions. This feature is particularly important for interactive applications and remote shell access.