iTunes in the Cloud overview
With iTunes in the Cloud, your iTunes Store purchases and iTunes music library can always be available on all your computers and iOS devices—wirelessly and without syncing.
Here’s how it works: When you purchase items from the iTunes Store, they’re stored in iCloud and downloaded immediately to any or all of your computers and devices that are connected to the Internet and set up to use iCloud.
If you subscribe to iTunes Match, you can store your entire iTunes music library in iCloud—including songs you imported from CDs and purchased from places other than the iTunes Store—and play those songs on any of your computers or devices whenever you want.
Automatic downloads and downloads of past purchases are available to all iTunes Store customers. To use iTunes Match, you need to subscribe to it in iTunes.