QUIT

The QUIT command is used to terminate a client's connection to the server.

Disconnect from Server
Usage: QUIT [<message>]
<message> An optional message indicating the reason for quitting.

When a client issues a QUIT command, the server closes the connection and removes the client from all channels they are currently in. If a quit message is provided, it is sent to all affected channels and users.

(See section 4.1.6 of RFC 1459, 3.1.7 of RFC 2812)