irssi/docs/help/in/kick.in

@SYNTAX:kick@

This command "kicks" the specified user off of the specified 
channel. It is typically used to remove troublemakers, flooders, 
or people otherwise making a nuisanse of themselves on the channel. 
The reason for the kick is recommended, but not required by the IRC 
servers.

If the <channel> is omitted, removes the nick from the current
channel.

The default alias for /KICK is /K.

See also: KNOCKOUT