A good place to start would be this essay: https://www.gnu.org/philosophy/free-sw.en.html https://www.gnu.org/philosophy/free-sw.en.html - which he wrote becaus

A good place to start would be this essay: https://www.gnu.org/philosophy/free-sw.en.html https://www.gnu.org/philosophy/free-sw.en.html - which he wrote because the term "free software" (as you correctly observe) would be too fuzzy. RMS has his faults but ambiguity is not one of them. He really bends over backwards to be careful about explaining what he means.