Hidden city ticketing is a flight-hacking tactic, similar to throwaway ticketing, where the traveler buys a roundtrip ticket with a layover, and the layover is the intended city of travel. The rest of the ticket is not used. This is for when a ticket with a layover at the intended destination is cheaper than a booking the flight right to the intended destination.
For example, let’s say I’m looking for tickets to Panama City, Panama (PTY). At the same time, I look for tickets to Bogotá, Colombia (BOG). The tickets to BOG were about $577 at the time, while tickets to PTY from JFK were about $640. I find a ticket to BOG for $577 on United, which has a layover in PTY. Only problem is, if I didn’t fly leg 2 and 3 of this flight, they wouldn’t let me fly home from PTY on leg 4. This works better on one way itineraries. Always be careful (and never check bags!)!