I just completed an article entitled Introduction to Open Source and Free Software. It is the most comprehensive introduction to Open Source, Free Software, and the differences between them - that I am aware of.
The article explains the key terms, definitions, people, organizations, and acronyms of Open Source and Free Software in a way which both non-technical and technical people can understand. Plus it offers an explanation of "What is Open Source and Free Software?", "Why does this matter?", and "Does this approach really work?". There are also plenty of links out to other sites for readers to dig deeper on the topics of interest to them.
The article is scheduled to be published in the September 2000 issue of The Bell newsletter. It is also available online at www.technodemocracy.org/people/tgw/docs/ossfs.html.