Cloud has a lot of different meanings these days so it's nearly impossible to really define it, but it is possible to think of them in various different contexts:

- Consumer cloud or SaaS for consumers (gmail, rdio, facebook, etc) - SaaS for business (salesforce, box, etc) - Cloud Infrastructure Services (amazon, rackspace, etc) - Cloud Application Services - higher level services on top of cloud infrastructure (heroku, iron.io, mongolab, papertrail) - Private clouds (which can include several of the above) - etc...

In this article I'm referring to cloud application services because those are the high level services that just take a couple lines of code and a couple of minutes to configure and use.