Here's a basic introduction to the definition of "free software" as defined by the Free Software Foundation. This was a spur-of-the-moment video; questions and comments are welcome!

TEDx Talk by Richard Stallman on this topic: https://www.fsf.org/blogs/rms/20140407-geneva-tedx-talk-free-software-free-society
FSF's Definition of Free Software: https://www.gnu.org/philosophy/free-sw.html
FSF Homepage: https://fsf.org/