Usage: DEOP <#channel> [<nick>]
This will deop a user or yourself in a channel, but the mode change is done by the server, you need to have AOP or higher access to the channel to use this command. If no nick is given, it works on yourself.
It's particularly useful if you are not opped but need to deop someone else or yourself quickly.
/deop #mychannel Zorgor
deop #mychannel
See also CMODE +o and DEVOICE.
This replaces the service command /CS DEOP.