For those unfamiliar with the terminology, there are two types of miles you earn with the big three US carriers. All miles you earn can be redeemed for free ti

For those unfamiliar with the terminology, there are two types of miles you earn with the big three US carriers. All miles you earn can be redeemed for free tickets. But only one type -- elite-qualifying miles ("EQM") -- also advance you toward the next level of status in the frequent-flyer program, and status is what gets you most of the nice perks. The other type -- redeemable miles ("RDM") -- are only useful to redeem for tickets, and do not count towards status. When airlines offer "bonus miles", with a few exceptions they are RDM, not EQM. RDM are also a heavily deflationary currency, because airlines issue them by the bucketload, and then adjust their redemption charts regularly to account for how many they've given out. (the biggest exception is booking into premium fare classes like first class or business class, which typically does apply a multiplier to the earned EQM) Achieving status typically requires: * A certain number of EQM in a year, or a certain number of segments flown in a year * And a certain minimum amount of actual money spent (elite-qualifying dollars, or "EQD"), as a measure to prevent people racking up huge amounts of mileage on bargain-basement tickets, and then trying to claim status with all its perks There are typically four published levels of status; American calls them "Gold", "Platinum", "Platinum Pro" and "Executive Platinum". Delta has Silver, Gold, Platinum and Diamond. United has Silver, Gold, Platinum and 1K. Perks start out pretty basic at the lowest levels, but get pretty serious (and pretty nice) at the top tier. There are also unpublished levels above that, typically by invitation only, for people perceived as ultra-high-value customers. American's version is called Concierge Key, Delta's is called Delta 360, United's is Global Services.