The promise of the cloud is simple: You have all of your stuff — your photos, your documents, and even preferences for apps — available anywhere, anytime, from any device.
You don't think about this. You just know it's up there, in that metaphorical "cloud" (really, a bunch of data centers accessible via the internet).
If you want to show a friend a snapshot from 10 years ago, you've got it right there on your phone or computer. You want to retrieve a Word document? Yes, you can edit it right on your tablet. Your notes, your playlists and your calendar? They're on every device you've got.
This is largely possible now, but it's not because of one überservice. It's because of a number of services, from different companies — competing companies, in fact. And that term, "the cloud," is something of a misnomer, as it suggests something up in the sky.
But there is not one cloud.
There are many clouds.