InQueue automatically does two things while you are queued for a dungeon:
1. Declines group invitations and whispers the inviter with a message saying you're in queue and cannot group at the moment.
2. Replies to /whisper's and /say's requesting to join your group with the same message as above.
Useful if you are a mage or do dailies while waiting in queue.
/inqueue or /inq brings up a list of commands:
/inq list: Lists autoreply trigger keywords (partial matches are okay). (Default: "join", "group", "grp", "party", "inv", "tele", "port")
/inq add <keyword>: Add <keyword> to the list of autoreply trigger keywords.
/inq del <keyword>: Delete <keyword> from the list of autoreply trigger keywords.
/inq ignoreguild: Toggles auto-declining group invites from guildmates. (Default: on)