Everyone wants to talk about "the cloud" right now. For technology industry watchers, cloud computing is a cocktail party conversation term du jour. For IT leaders, though, it's time to be careful: This whole discussion about cloud computing gets tricky, because cloud computing means different things to different people. And when your colleague or boss drops an article about "cloud computing" on your desk and says, "What's in it for us?," you'd better understand what to tell him.When companies like Salesforce.com talk about cloud computing, they're talking about using applications via "the cloud," which means via the Internet instead of via the traditional enterprise software model. So when Salesforce.com talks about "the cloud" they're of course also talking about Software-as-a-Service (SaaS), also known as "on demand" software. Different names, same idea. But Salesforce is taking the idea a step further now, with its Force.com platform, essentially a platform that's accessible on-demand to help other software developers create and distribute applications. They call it "platform as a service." As ZDNet blogger Dan Farber and others have noted, Salesforce.com CEO Marc Benioff and Web whiz kid Marc Andreessen were waxing rhapsodic this week about the future of software development via the cloud. When Google talks about the cloud, they're talking about banding huge numbers of computers together (something that Google knows a little about) to let researchers in those frighteningly computing-intensive fields like medical and security research do massive calculations. Sounds a lot like "grid computing" doesn\u2019t it? The basic idea tackles the same problem, but Google's vision will band together much more raw computing power. At its simplest, you can think of the cloud like this: Many, many multicore PCs and servers working together over high-bandwidth networks.IBM's got a similar idea, for an offering they call "Blue Cloud," and they want to help customers use huge amounts of combined computing power via the Internet to slice and dice their massive data sets better and faster. It's mostly talk right now, but look for IBM to dial up the volume on this idea later this year.When Amazon talks about the cloud, they are talking about their Elastic Compute Cloud (EC2) service. When I first heard Jeff Bezos talk about this, at an MIT Emerging Technology conference in late 2006, I thought the idea was simply brilliant. Need extra computing power? Just tap into Amazon's huge data centers, overflowing with compute power. Buy only what you need. Get server access on demand, for whatever project you like. Amazon makes extra money from infrastructure that they have to have on hand anyway to support their mind-boggling e-commerce operations.Great idea. Made perfect sense. In an era when many of us were already comfortable using applications via the Web, the time seemed right. The tech industry types got the idea, too: For example, Red Hat used Amazon's EC2 to share the public beta of its Enterprise Linux platform in fall of 2007. Funny thing though: It's early 2008 and many CIOs have not gotten their heads around this concept, never mind gotten comfortable with it. Industry analysts love to point to Amazon's offering and chat about what it will mean to IT's future. Think much smaller enterprise data centers. Think tons of data stored in the cloud, ready to be mashed up in many ways on demand by business users. That's the big picture, and it's an interesting one. But there are a lot of pixels that have to be filled in before most IT leaders can picture it in their own company.When I was on a conference call recently with about 30 CIOs from some big-name U.S. companies, and the moderator asked if anyone was using Amazon's Elastic Compute, you could not hear a peep. Anyone even seriously considering it? Silence, again.What's the problem? Some CIOs still have not bought into the SaaS concept, and some have good reason for that stance. Whether SaaS works ROI-wise depends on your IT group, budget, need for customization, and a host of other factors.CIOs who worry about security and compliance issues with regards to SaaS have told me that they have these same concerns, but even more so, when you start talking about the Amazon vision of the cloud. That's a hurdle that Bezos, Benioff and the hundreds of application developers who plug into Salesforce.com's force platform will have to jump. I wouldn\u2019t bet against their ability to do so in the long term. But it will take time.There's one more aspect to "the cloud" that IT leaders should understand. As we recently reported, software industry upstart rPath is using virtualization technology to help software vendors move further away from traditional software development. rPath offers services and infrastructure that lets software vendors dish up software to customers inside a virtual machine. That self-contained VM can live on a physical server or that VM can live offsite, accessed via "the cloud." That is, via the Internet. This model presents a lot of compelling benefits for both users and software vendors. (rPath, incidentally, is an Amazon EC2 customer.)Many of you are now realizing that you know more about cloud computing than you'd thought. If you're using a SaaS app in your enterprise, you're using "the cloud." If you run your personal life via Google tools, you're tapping into "the cloud." If you're using Amazon's EC2 service for your enterprise, e-mail me. I want to hear your story and share what you've learned with other CIOs. As for the industry buzz on "the cloud," it's here to stay. You're going to see "the cloud" in plenty of articles in the mainstream press. This term is not likely to pop out of Katie Couric's mouth anytime soon, but you'll probably hear some people talk about it without having any good idea what it is. By all means, IT leaders, be ready when these folks stop by your office to chat.This all reminds me of that vague, jargon-laden "information superhighway" talk back in the day when people didn\u2019t understand "where" the Web was. Let's hope we don\u2019t take so long to get our heads out of the clouds this time.