what is itunes plus

There is no such thing as iTunes Plus.

Where did you come across this reference? Perhaps it was AppleTV+ ?

Kluong,

iTunes Plus was the name Apple gave to its song format when it first started selling non-DRM-protected music tracks, which was around 2009. It meant AAC audio format, 256 kbps coding rate.

Now, all the music downloads sold in the iTunes Store are in that format, and they no longer use the term "iTunes Plus."