The phrase "free roundtrip" means that a person can travel to a destination and then return back to their starting point without having to pay for the transportation. Full definition
That many miles could translate into free roundtrip airfare. (creditcards.com)
It was cheap too with the Canadian dollar being so low compared to the US dollar and we each used 25k Delta miles for free roundtrip flights. (mytraveltools.com)
Two Air Canada pilots listen to the reasons why patrons won't be returning for the holidays, then surprise them all with free roundtrip tickets. (canadianbusiness.com)