Here is the link from which I cut and pasted the info:
From Wikipedia, the free encyclopedia
For other uses, see frequent flyer (disambiguation).
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A frequent flyer program (FFP) is a loyalty program offered by many airlines. Typically, airline customers enrolled in the program accumulate frequent flyer miles (kilometers, points, segments) corresponding to the distance flown on that airline or its partners. There are other ways to accumulate miles. In recent years, more miles were awarded for using co-branded credit and debit cards than for air travel. Acquired miles can be redeemed for free air travel; for other goods or services; or for increased benefits, such as travel class upgrades, airport lounge access or priority bookings.
The first modern frequent flyer program was created at Texas International Airlines in 1979. American Airlines' program was a modification of a never-realized concept from 1979 that would have given special fares to frequent customers. It was quickly followed later that year by programs from United (Mileage Plus) and Delta (SkyMiles), and in 1982 from British Airways (Executive Club).
Since then, frequent-flyer programs have grown enormously. As of January 2005, a total of 14 trillion frequent-flyer miles had been accumulated by people worldwide, which corresponds to a total value of 700 billion US dollars.