What, exactly, do we mean by "SaaS?"

"Software as a Service" has, obviously, crossed over into mainstream usage among techies. But that doesn't mean that we really have a clear idea what we mean when we use the term, does it?

Traditionally, most people think of Salesforce.com when they think of "SaaS." Namely, delivering an enterprise software application as a service. That beginning definition has given rise to literally *hundreds* of SaaS application providers -- from the general to the niche. I've even seen SaaS providers built specifically for compliance in the oil and natural gas industry.

Lately, though, we've seen a move to "the platform as SaaS" -- with notables like Salesforce.com getting into the game. Further, we've seen a growth of "infrastructure as a service," as Amazon Web Services has brought their spate of offerings to the table.

All of that leads us to companies like Coghead. Coghead is built on top of Amazon Web Services and is delivering a "drag and drop" application building environment. Obviously this is "software" being delivered as a "service," but it also seems like we've begun to stretch the original conceptions of "SaaS" far beyond their limits. Will all software (and its accompanying applications, platforms and infrastructure) move to the "cloud?" If that is the case, then Nick Carr's new book (The Big Switch) should be on every SaaS user or vendor's reading list.

And *every* vendor will (over time) become a SaaS vendor? Is that the future of software as we know it?