Multi-User or Multi-Site or Network?
With the release of WordPress 3.0 (now in v3.0.1 release) WordPress MU became an integrated part of the standard WordPress code base. At the time of initial installation we can now choose which style of WordPress we want to run: single site stand-alone mode or multi-site network mode. Along with this choice comes a little confusion in what we should be calling things.

We need some clarification in the terminology that has sprung up over the years as WordPress has grown and matured. Originally WordPress was a blog. That was easy. Then it gained the ability to add pages and other non-blog content. Was it still just a blog or was it actually a website? Then came extended content and the associated management facilities. Was it just a website or was it a true content management system (CMS)? Now it has single site or a multiple site capability withing the single installation.
So is it now multi-site or do we continue to think of each website as a blog? And what’s all this network stuff? WordPress now refers to the multi-user (MU) capabilities of the latest WordPress package as a network, as in “network of blogs or websites”. Sure, WordPress can still be installed and used as just a blog — some blog! — but it is more often than not installed as a complete multi-page, multi-function, website; a full content management system. And, when you expand the installation to support multiple,simultaneous, individual, independent, websites or content management systems, then the term network certainly applies.
The term website or just site is, I believe, preferable to blog for an individual installation. The term network is great for an installation comprised of multiple websites under a single WordPress umbrella. As we move ahead with the new structures these terms will become more common place and more comfortable in normal use.
But whatever you call it, WordPress is undoubtedly the very best choice for many varied website needs. I’ll be glad to help you decide how to best utilize it for your specific online needs.