iCloud ?
In simple language?
Applekeep a record of everything that every Apple user does ... where they go, what they search, what they look at, what they listen to, etc etc etc ...
They OWN you, in a way that Big Brother in 1984 could never dream of.
And by having an accurate record of the life patterns of hundreds of millions of users, they can target their hardware releases, knowing in advance how many people are waiting for it because they have a record of yourGoogle searches.
Instead of releasing the next iPhone, the iPhone6, they add a few crap things to the last one, and call it the iPhone5, because their information has told them that tens of millions of people will buy a 5, and then ALSO buy a 6 ... so they double their money.
Or ... you can be sensible and opt out of the iCloud.