"FairPlay is a digital rights management (DRM) technology developed by Apple Inc. It is built into the MP4 multimedia file format as an encrypted AAC audio layer, and was used until April 2009 by the company to protect copyrighted works sold through iTunes Store, allowing only authorized devices to play the content."

"FairPlay-protected files are regular MP4 container files with an encrypted AAC audio layer. The layer is encrypted using the AES algorithm. The master key required to decrypt the audio layer is also stored in encrypted form in the MP4 container file. The key required to decrypt the master key is called the "user key".[1][2] When a user registers a new computer with iTunes, the device requests authorization from Apple's servers, thereby gaining a user key. Upon attempting to play a file, the master key stored within the file is then matched to the user key, and if successful, allows playing.[2] FairPlay allows unlimited music burns to CDs and unlimited music synchronization to iPods, but restricts listening to three Mac computers.[3]"

I still don't understand what would "FairPlay applications" entail? Anyone care to explain further?