Open Jaw

Seattle to Paris to Istanbul return to Seattle is not an open jaw. An open jaw is a two-way flight, with a return from a different location than the airport you flew into. For example, Seattle to Paris, return from Amsterdam. The "open jaw" part would be from Paris to Amsterdam, i.e., it's not part of your air ticket, so you arrange other transportation for that portion of the trip. Like, you could take a train to Amsterdam from Paris. Anyway, either for an open jaw, or for the itinerary you want, you would choose "multiple destinations" on travel sites such as Expedia. Expect this to cost more than an open jaw, as you are basically buying a bunch of one-way tickets. But, there may be some discount, depending on the airline and available seats.

Choose "multi-city" instead of "round trip" when booking. You may be able to book several flights this way. Just be careful to keep your dates straight.

An open jaw does not have to be two one way though that is what most people do. Into one city, home from another. You can do a triple leg easily - into Paris, onto Athens and home from there. Over TG we are flying to New York, back to Chicago, and home to Denver - very reasonable.

Thanks for helping with my learning curve!