The amorphous term “cloud computing” includes lots of different service-delivery models — everything from managed services, to utility computing, to software-as-a-service (SaaS), as Infoworld outlined in a useful cloud-computing primer this week. And within these cloud subcategories, definitions are vague, too.

Consider platform-as-a-service (PaaS). Some are defining Google unveiled Google App Engine as a prime example of PaaS. But they also are lumping Salesforce.com’s Force.com platform into this category, as well.

Microsoft is readying a hosted application platform, according to my sources, that sounds a lot like Google’s App Engine. BizTalk Services and SQL Server Data Services are allegedly among the components of this still-to-be-announced Microsoft-hosted service, which will be aimed at developers  who want to use Microsoft’s development/deployment/hosting platform as a launch pad.

But Microsoft also is working on another PaaS offering (which its officials are loath to call “PaaS”) that is more akin to Force.com. Microsoft  officials first discussed Microsoft’s “Titan as a platform” strategy over a year ago. This year, Microsoft officials began referring to Titan the platform as “xRM” (though it sounds like this isn’t the final name or brand).