Microsites Explained at Wikipedia

I was talking with a client today about a microsite linked to a print advertisement. Microsites are landing pages for specific content. A person who visits a micro web site arrives because they have probably encountered content -- print content, such as an ad or a case study or a white paper, or an article, or a link from the organization's main page or another third-party website -- and they want to learn more. The opportunity at the microsite is to focus just on that particular topic and perhaps induce the reader to fill out a form in exchange for obtaining more information.

In explaining the concept, I was pleased to find that Wikipedia has a good -- and brief -- article on micosites. The term is pretty much synonymous with "minisite," which also bears reading in Wikipedia.