Frequent flyer miles

A frequent-flyer program (FFP) is a loyalty program offered by an airline.

Many airlines have frequent-flyer programs designed to encourage airline customers enrolled in the program to accumulate points (also called miles, kilometers or segments) which may then be redeemed for air travel or other rewards. Points earned under FFPs may be based on the class of fare, distance flown on that airline or its partners, or the amount paid. There are other ways to earn points. For example, in recent years, more points have been earned by using co-branded credit and debit cards than by air travel. Another way to earn points is spending money at associated retail outlets, car hire companies, hotels or other associated businesses. Points can be redeemed for air travel, other goods or services, or for increased benefits, such as travel class upgrades, airport lounge access, or priority bookings.

Frequent-flyer programs can be seen as a certain type of virtual currency, one with unidirectional flow of money to purchase points, but no exchange back into money.

Though United tracked customers as far back as the 1950s, the very first modern frequent-flyer program was created in 1972 by Western Direct Marketing, for United Airlines. It gave plaques and promotional materials to members. In 1979, Texas International Airlines created the first frequent-flyer program that used mileage tracking to give 'rewards' to its passengers, while in 1980 Western Airlines created its Travel Bank, which ultimately became part of Delta Air Lines' program upon their merger in 1987.American Airlines' AAdvantage program launched in 1981 as 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 Airlines (Mileage Plus) and Delta Air Lines (SkyMiles), and in 1982 from British Airways (Executive Club).

...
Wikipedia