"Q: "What is a folk song?" A. It's a song."
What is 'Banks of Sweet Primroses' - It is a folk song; What is 'Come Into The Garden Maud' - it is a parlour song by Tennyson.
Song = general, folk = specific.
We specify our requirements so we don't end up with a tin of mulligitawney soup when we'd rather have mushroom.

"Has this word stayed the same?"
According to my dictionary it has.
Gay (gay) adj. gayer, gayest.
1. Showing or characterised by cheerfulness and light-hearted excitement; merry.
2. Bright or brilliant, especially in colour.
3. a. Homosexual, b. Of, pertaining to, or for homosexuals. 4. Full of or given to social or other pleasures.
5. Rare. Dissolute; licentious.
As with many words it has several definitions, all totally independent of and unaffected by one another.

"I just get the impression that some people are more interested in the word and the definition than they are in the music. "
And I get the impression that some people are constantly attempting to seperate the music from its origins, its form, its social, historical and cultural implications in order to put bums on seats.
As far as I'm concerned, people are welcome to become involved in folk music from whatever aspect they choose, as a listener, as a performer, particular or easy-going in what they listen to or play.
Some of us have stretched that activity to include taking a closer look at what we are involved in.
Yes, it's about the music, but it's also about the people who made it and kept it alive, and passed it down, about the circumstances and conditions that gave rise to it, and all the other cultural baggage that the music carries with it.
IT IS NEVER JUST ABOUT THE WORD.
Jim Carroll