Question: The company I work at recently hosted a web service in Windows Azure and announced that. Now trade online magazines say lots of meaningless stuff like "company X moves to the cloud", "company X drops desktops for the cloud", etc.

Looks like there're lots of materials out there (starting with [Wikipedia](http://en.wikipedia.org/w/index.php?title=Cloud_computing&oldid=459932705)) that are very lengthy and talk a lot about "services" and "low entry price" and other stuff but I've read all that and don't see how they could be helpful for a layman in drawing a line between a service in a cloud and Stack Exchange that is also a service but is run on brick-and-mortar servers in a colocation.

Now from my experience with Windows Azure the real difference is the following. With a cloud the service owner rents hardware, network bandwidth and right to use the middleware (Windows 2008 that is used in Azure roles for example) on demand and also there's some maintenance assistance (like if the computer where a role is running crashes another computer is automatically found and the role is redeployed). Without a cloud the service owner will have to deal with all that on his own.

Will that be the right distinction?

Answer: 
No. Cloud computing is not merely a way to rent resources.

Cloud is all about services that:

* are delivered over the network (possibly the Internet)
* are fully controlled by API
* are fully automatable and automated
* require no human interaction for control
* are delivered as a commodity
* are billed like a utility: for measured usage
* require no capital expenditure or up-front payment
* have seemingly infinite capacity
* permit at-will immediate allocation of arbitrarily many units of the service
* permit at-will immediate disposal of arbitrarily many units of the service

NIST has a [full definition](http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf) of what a cloud service is.
Cloud computing does not only provide resource renting.

It also offers a fault tolerance layer, should the rented resources fail. Serious cloud providers work hard to deliver a service without interruption.