If you’re not heavily involved in the development or use of free and open source software, I imagine it can be very hard to understand the subtleties and the importance of free (as in liberty and speech) software versus open software that you can use for free (as in gratis and beer). For most software users, it’s probably not the most important distinction in their lives for them to grasp. But for many users, and especially for developers, it is very, very important.
Karl Fogel wrote a very nice article at O’Reilly OnLamp.com that does an excellent job of explaining the difference between the two, and why both are very important. If you ever wanted to know more about these software movements, I highly recommend that you read this three page article. Karl did a great job of explaining the history, intellectual property concerns, and impacts on users and developers.