The Cupertino firm announced at the WWDC Monday June 06, 2011, the service that many expected.
To understand what is iCloud, you must already know what that is cloud computing in general. Although it is often compared by a hard drive on the internet, this metaphor does not completely correspond to reality. Cloud computing is not a storage service, but a synchronization service.
The Apple service is no exception.
iCloud allows you to automatically send this cloud any information contained on any of your devices. You take a photo with your iPhone, it is automatically sent to the cloud. If you turn on your iPad or iMac (or PC) which is also configured with iCloud, the photo is automatically recovered. Without any action from you. It doesn't work only with the photos. Music, contacts, calendars, apps and many others are well synchronized between all your devices. There is no need to connect your devices together to transfer the data, everything is automatic.
This service will be available fall 2011 in same time as release of the latest firmware "iDevices", the highly awaited iOS 5, and will be free except for the music service.
We just need to wait until the release.