In essence, Free software and Open Source software mean the same thing. "Open source" is just used to market "Free software". How you misunderstood "Free" Software to be free in cost terms, many would misunderstand. Hence the term Open source was coined.
But the whole ethical VS practical issue I realized only after attending the Public Lecture given by RMS... and that is a huge difference between the two. It changes the entire perspective to using the software.