topic (to query topic in current channel)
topic <channel> (to query topic in stated channel)
topic - (to unset topic in current channel)
topic -<channel> (to unset topic in stated channel)
topic <new topic> (to set topic in current channel)
topic <channel> <new topic> (to set topic in stated channel)

Each irc channel may have a “topic of discussion” which is displayed to new channel members when they join. The “topic” may be anything at all, it does not have to actually be the topic of discussion.

The first two usage forms query the topic for a channel; generally you must be a member of a channel to query that channel's topic.

The second two usage forms unset the topic for a channel; this is nothing more than setting the topic of a channel to the empty string. The channel “has no topic” after the topic is unset.

The last two usage forms set the topic for a channel.

The maximum length of channel topics is a server setting and as such, varies from server to server. A common limit is 80 characters.

If a channel has mode +t set, you must be a channel operator to set or unset the channel topic. All channel members can query the topic of a channel at all times.

Networks that support the TS (TimeStamp) protocol or TS-workalikes keep the nick!user@host of the person who set the topic, and the time that the topic was set. This is provided in a 333 server numeric.

To set a new topic on your channel:

    /topic #blah Welcome to #blah, a very serious channel.
    or
    /topic Welcome to #blah, a very serious channel.

To view the current topic for your channel:

    /topic #blah
    or
    /topic

To unset the topic for your channel:

    /topic -#blah
    or
    /topic -