While I haven't done one, it seems to mostly be a mega-vacation.

Much like a cruise that stops in various ports of call, you build an RTW itinerary to visit the places that you want to spend some time.

You might start in London for a few days, then go on to Egypt and see the pyramids, catch another flight to India to catch up on your spiritual guidance, fly on to Hong Kong to stock up on DVD's, and wrap it up with a week on the beach in Cabo San Lucas before heading back to New York.

I think you can string together a large number of stops with the general delimiter being the number of miles you fly in total (which determines the price). The big rule is no backtracking (including specifically a limit of 1 Atlantic and 1 Pacific crossing), and some limits on the number of stops on your home continent.

Now, some really travel often enough that they use these tickets as a pricing tool, structuring complex nested itineraries combining multing RTW itinieraies with various point-to-point and round-trip itinieraries.

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robb is clearly within the margin of sampling error - Googlism