Apple used today's WWDC keynote address to announce a brand new service called iTunes Match - which was also referred to as "iTunes on the cloud."
iTunes Match will scan your iTunes Library and match songs to an upgraded, 256kbps AAC DRM-free file on Apple's iCloud server. The service will cost $24.99 per year but it remains to be seen what will happen if you stop paying the annual subscription fee.
Apple touted 'Match as a huge advantage over competing services from Google and Amazon, because while they can take "weeks" to upload your library, iTunes Match takes "just minutes."
Apple also touted the service as having the "same benefits as music purchased from iTunes." Presumably this means that you'll be able to re-download tracks and see your music history on all of your devices.