Web services, SOA, everything-as-a-service: what are all these terms?  What do they mean to you?  Here’s a list of definitions as I see them:

Service Oriented Architecture.  a way of describing a business model that uses cloud computing.

Cloud Computing
The use of Web Services.

Web Services
Software or data served over the Internet as an ongoing service rather than a custom-made or out-of-the-box piece of software or dataset (delivered, say, on CD)

Data as a Service.  Outsourcing data managment to “the cloud” – either “public” data (such as street names) or private data (such as stock lists).

Desktop as a Service: This term hasn’t really caught on due to DaaS being generally reserved for “data as a service” or “database as a service”.  Desktop as a service is a rather more accurate term for the more buzzword-y “Operating System as a Service”; not a true operating system (which boots up the computer and manages a user’s hardware resources) but an online desktop which stores your preferences and basically acts as an interface for other web services, just like a normal desktop is a user intterface for traditional software and data.

Software as a Service.  Outsourcing software to a company “in the cloud” that runs the software, updates it, and allows business access to it for a charge.

Platform as a Service.  A piece of software delivered as a service that allows development of 3rd-party apps to “plug into” it.  Examples: Salesforce.com, Facebook.com

Lesser-known services under the umbrella “everything as a service”

Communication as a Service.  Delivering telecommunications, instant messaging etc. as a service over the Internet.  Telephony as a service, also known as “Voice as a service”, employs VOIP (Voice Over Internet Protocol).  Software and hardware can be provided as a service by providers.

Infrastructure as a Service.  Slightly tricksy one, this.  Can be taken as being similar to “Operating system as a Service” or “Desktop as a Service”, Infrastructure as a Service typically dishes up services centred around hardware as well as software.  Wikipedia tells us that “servers, software, data center space or network equipment” are all served in IaaS.

Monitoring as a Service.  Network/website monitoring delivered as a service.  Notifications of network or website problems delivered via SMS, email, etc.

Another term not really part of the Web 2.0 Buzzword Boom but still applicable

Utility Computing
Self-explanatory: providing computing services as a metered utility, in the same way that the services above are delivered as a service.

I know I’ve missed some and will update this list and make it more accurate on a rolling schedule.  This can be another DaaS: Definitions as a Service – not that I’d want to muddy the waters any more, you understand.

You can read here for a bit of talk about SOAP etc.