The topic command alone will display the channels topic. If the optional [New Topic] argument is given, the topic will be changed to the argument given, provided that the topic is not protected, or the user issuing the command is an operator on the channel.
Related: MODE
Examples:
`/TOPIC #AmIRC'
Will display the current topic on #AmIRC.
`/TOPIC #AmIRC Amigas Rule!'
Will replace the current topic of #AmIRC with the topic 'Amigas
Rule'