In general, airline miles programs allow you to accumulate airline miles based on purchases (or other actions). You can save these miles up and redeem them for free flights and other perks down the road. For example, once you accumulate 20,000 airline miles, this could be enough miles to afford a round-trip flight to any number of domestic destinations. These are also commonly referred to as "frequent flyer miles," so if you see this term use, don't be confused; they're interchangeable.