Points can also be redeemed for flights on more than 400 airlines. (travelandleisure.com)
So you buy the miles at a low price, which then when redeeming for flights at a higher value. (meinemeilen.com)
Typically, airline travel rewards cards allow you to redeem for flights with a particular airline and hotel rewards cards will let you earn free nights at one hotel brand. (mybanktracker.com)