Look it.

IP.

It means in progress.

That means that I am in the quest.

When you join and ask, "Where are you?", I'm in the quest.

I'm not in a tavern.

I'm not at the auction.

I'm not on my airship.

I'm in the quest.

Amazingly enough, if I put "In Progress" in my comment, that also means that I am in the quest. That may throw you off as it is actually spelled out, but I assure you it is synonomous with IP.

Next time, "Zerged," and why it is probably too late if you are trying to figure out which house the quest is in.