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Fare Rules contain airline-specific information about your flight, including advance ticketing requirements, blackout dates and other travel restrictions, penalties, discounts, and a range of other information.
A refundable fare may have some fare restrictions such as advance purchase or day of week application and in some cases may have a refund penalty but the fare in general is partially/entirely refundable.
An unrestricted fare has no fare restrictions such as advance purchase or day of week application but is fully refundable.
You can see them on the "Review your trip" page by clicking Fare Rules. See Reviewing the Trip Elements for details.
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A ticket will not be issued, and you will not be charged for the price of your flight itinerary until the trip is purchased. However, prices and seats are not guaranteed and a new price will be applied when the trip is purchased. This new price will be displayed on the Purchase page. See Putting a Trip on Hold for details.