Yup. BIS, including guaranteed minimum mileages, not RDM. Really even simpler.
More correctly, it's
base miles earned. That's BIS with guaranteed minimums on AA flight numbers, but can be less on some partners on some fares.
AA's
Upgrades page is very clear (emphasis added):
AAdvantage Platinum and AAdvantage Gold members earn four 500-mile electronic upgrades for every 10,000 qualifying base miles flown (including guaranteed minimum miles) during your membership year (March 1 or the date you qualify for elite status, through the last day of February). So, the more you fly, the more upgrades you earn.