CHANNEL MODE m

Usage: MODE <channel> +|-m
m - Moderation
Causes a channel to be moderated so only the operators and those users who are +v (voiced) can talk. UOPs cannot talk in moderated channels unless they are temporarily voiced or opped. Moderation is a good way to carefully control a channel.
If anyone starts causing problems you only need to remove their +v (ops should not be causing problems because they should be trusted, but if they do, then removing their status will fix things, although you might need to remove their entry from whichever op list they are on).
The downside to constant moderation is that there must be an op present at all time to voice new people or else they can't talk, and the channel may become temporarily unuseable. It also is tedious to voice every new user so that they can speak.
Although this can be accomplished by a bot. Moderation is usually reserved for channels that only wish to allow certain people to speak (events, lectures, etc.) or that wish to give different people the floor for a time (debates, storytelling, etc.).
Privilege: channel operator
Examples:
/mode #movies +m

CHANNEL MODE M

Usage: MODE <channel> +|-M [<channel>]
M - Moderation target
This mode is used in a forward moderated chat. If the channel is set to +m all the messages sent to the channel that cannot be viewed by other users will be sent to a +N channel that is specfied when the mode is set. +M and CMODE +N work together. The channel must be +m (moderated) for the messages to go to the receiving channel.
Privilege: network operator
Examples:
/mode #event +M #questions
See also: CMODE +m and CMODE +N