To sum it up - welcome to Trisquel.
Most users on the forums prefer the term of "Free Software", as we think of
it as an ethical issue.
It's about software that is free as in freedom of speech.
The 'open source' camp (best term I can think of) merely decides to let
others work on their code as well,
because they think it's convenient.
While in most cases Free Software and open source software are the same, the
idea is a different one.
I hope that explained it simply enough. In any case, enjoy your free
computing experience (assuming you got Trisquel to work)!