The Definition of Green is on my list of things to write about. InfoWorld's Ted Samson writes his definition, and provides good points.

A couple of final thoughts on this subject: First, if a vendor comes to your door hawking what it deems a green product, be sure to ask just what makes it so green.
Second, bear in mind that a product deemed green today will be considered wasteful and eco-unfriendly tomorrow. Technological advancement coupled with relativity is funny that way.
Finally -- and this is a point I'll keep making until my fingers ooze (the blogging equivalent to the expression "talking until I'm blue in the face"): Green products alone simply can't make your company green. A blueprint for long-term sustainability is a must, and the products you employ are but a piece of the puzzle. Deploying virtualization in your datacenter may very well help you make better use of your resources in the short- or midterm. It may also reduce your company's carbon footprint. But you most certainly need to plan beyond that for the sake of your organization's future prosperity -- as well as for the sake of the environment, if that is, indeed, a concern for your company.

This definition fits well with another post.