What is 'folk music'? And can folk music be called just 'folk'?
Folk music is a term for musical folklore which originated in the 19th century. It has been defined in several ways: as music transmitted by word of mouth, as music of the lower classes, and as music with unknown composers. It has been contrasted with commercial and classical styles. Since the middle of the 20th century, the term has also been used to describe a kind of popular music that is based on traditional music. Fusion genres include folk rock, electric folk, folk metal, and progressive folk music.
Bob Dylan and Joan Baez are two better known "folk musicians"

Leaving the "music" out of "folk music" can be too vague. The word "folk" has it's own meanings (typically rural people)

My folks = my parents
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I think it can work like "pop," although "pop music" is less often used.

It depends on the conversation.

"This guy used to be into rock 'n' roll, but then he switched to folk."

When the parameters of the conversation are established in this way, "folk music" is not required.

What kind of music do you like? (reply) I like folk.

I often hear this sort of thing. Of course, it's conversational.
VorparBob Dylan and Joan Baez are two better known "folk musicians"
I used to like Burl Ives, before he switched to acting. [H]

(Shows you how long I've been around!) Emotion: big smile
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I am so excited to listen to The Staves' new album. I've read that it's great. Their music is so unique and real.