What is iCloud?
iCloud stores your music, photos, apps, calendars, documents, and more. And wirelessly pushes them to all your devices — automatically. It’s the easiest way to manage your content. Because now you don’t have to.
http://www.apple.com/icloud/what-is.html
iCloud includes:
- iTunes in the Cloud
- Photo Stream
- Apps, Books, Documents and Backups
- Contacts, Calendar and Mail
(this is the MobileMe component)