How do I know what iTunes credit is for?
From https://discussions.apple.com/message/11510256#11510256


  It means that your next two purchases of that type won't be charged to a credit card or count against a gift card balance. They are sometimes granted by the iTunes Store staff.


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From https://answers.yahoo.com/question/index?qid=20100207142341AA3Kh6k


  It means you can get one[in your case 2] song download using that credit.


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From http://forums.macrumors.com/threads/itunes-is-displaying-5-credits-next-to-my-email-address-in-store-what-does-it-mean.1478823/


  5[in your case 2] free downloads. Did you report any problems with a purchase to them recently? They give them out for that kind of thing sometimes.


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