In the old days (I don’t really recall when exactly), techies used the term “cloud” – and back then it meant the network, specifically the WAN (wide area network). So, we would draw a picture on the board showing site A and site B and in between was this cloud (the network cloud). We didn’t know how we got from A to B and didn’t care — or if we did, we knew that the vendor, e.g. AT&T, could change it.
Now, “cloud” has a new meaning, stemming from cloud computing. One can now have application-as-a-service, platform-as-a-service, or infrastructure-as-a-service. An example of application-as-a-service cloud computing before such terms existed: webmail. Once, we stopped downloading e-mail from e-mail servers and just used some web interface from Yahoo or Hotmail, and the like, we moved into Cloud Computing. Those web servers are somewhere and can be moved without us knowing it.
So, “cloud” is just a way of saying, the technical resources/service is out there and the service is what is important not the “where”.
I’ll leave the different types of cloud computing – application-as-a-service, platfrom-as-a-service, and infrastructure-as-a-service for another day… Comment if there is specific interest…