When we talk about Free Software, we are talking about freedom, not price (Free as in "Free speech", not "free beer"). We are talking about software which grants users freedoms which we believe are essential. They are fully specified by the DebianFreeSoftwareGuidelines, but basically it is about the freedom to run, modify and distribute the software.
The English meaning of the word free, as in "free speech" refers to the same concept of the Latin word libere, meaning freely, openly, frankly, while the English meaning of free, as in "free beer" relates to the Latin word gratis meaning in exchange for nothing.
Selling free software is not an oxymoron: there are many places where you can buy Debian CDs. Please consider making a donation with your purchase! For as little as the cost of pressing the CDs -- often around US$8 -- you can have a 6-CD set of DebianPotato, and feel good about yourself making a donation to this wonderful project. Sure beats the price of Microsoft Windows, doesn't it? --- Dr. Shahid Akhter
Collectively, we refer to those who are actively working and advocating Free Software as the FreeSoftwareCommunity.
For a quantitative analysis of the advantages of free software by an exhaustive review of published studies, analyses, and news stories refer to David Wheeler's "Why Open Source Software / Free Software (OSS/FS)? Look at the Numbers!".
"The continued freedom to create and use free software is always in danger. Unfortunately, some interests seem to use the tragic events of September 11, 2001 as an excuse for wide-ranging infringement on civil liberties, some of which may threaten the very ability to create free software at all." - from https://kernel.org -> see PoliticalActivism
The debian-legal mailing list has long debates over which software is licensed to grant users's freedom and which is not. Often, common hypothetical tests are applied to help clarify a CornerCase that helps define Free software. The DissidentTest and the DesertIslandTest are two examples.