A hidden city (or more aptly, a "hidden city fare") allows one to fly from Point A to Point B cheaper by buying a ticket that says Point A to Point C with a connection in Point B. For example, I've flown from Boston to Los Angeles on AA in First Class for about $800 one way by buying a ticket that says Boston - Los Angeles - Las Vegas. I then just throw away the ticket for that last segment. (The fare BOS - LAX in first class if I ticketed it "correctly" is more than double that!). I've also had great luck with Boston - Houston - New Orleans on CO (First Class with this routing, throughing away the Houston - New Orleans segment is cheaper than coach on Boston - Houston). This, of course doesn't work if you want to check any bags, and is a diaster if your flight is cancelled and they want to re-route you. It's a by-product of the hub system (the hidden city is almost always an airline's Hub) - and some airlines threaten all kinds of bad things if you take advantage of it. It also doesn't work for discounted tickets - no roundtrips here - this is purely a way to get a business ticket cheaper.