What are iTunes song credits?

[RamMurthy5s]

I've noticed that iTunes song credits - 4 for my  ID when I was browsing through the AppStore. Someone tell me what does that mean & how to redeem it.

 

[Ledsteplin]

What's song credits shown in our  ID

You saw this in the App Store? You sure it wasn't in the iTunes Store?
It means that the iTunes Store has given you credit to download four songs at no additional charge. Just purchase songs normally and it should use those credits automatically.
There's probably several possible reasons for the credits. I know sometimes when you purchase an album say for $11.99, then the price is reduced to say $9.99 at about the same time, you may get a couple of credits. Also could be related to special album deals.