I think that we all agree that it's about time to release the details of eUpgrades. With more and more unimportant tidbits coming out about next years' Top Tier program, like the 10K/5 seg. req., and the recent tweet by Air Canada posted by YEG USER (define GO FAR and get the chance to win 10 eUpgrade credits).

Now, all together:
WHAT IS AN eUPGRADE CREDIT?