Channel

There are various ways to communicate in-game: using tells for communication between players; say, which outputs to any PC in the same room; yell which applies to the current area; globals which allow for anyone who has that channel toggled on to see; compose for a message-board style persistent notes; and more.

From "help channel:"

Channel:

Usage: channel <channel name> <message>

The channel command attempts to use a given channel. This command is very 
useful when trying to use a channel that has a similar name to that seen 
elsewhere in other commands.

For more information, see: help display channels

The way this command is written is useful, as there are cases in which a channel name is close or even part of another command, skill, or spell. You can send a global message on gossip for instance by typing "gossip message" but also "channel gossip message"