On a forum like this you will get definitions that refer to things like tunes (songs) with no known author, oral transmission, songs that have been subjected to a kind of Darwinian selection known as the "folk process" etc. etc.

Then you go to a folk club and, yes a great many of the songs that are sung have been composed by that most prolific of authors "Trad". But the rest of the songs sung have been composed within living memory and their authors are known.

At that point you shrug your shoulders and settle back to enjoy the music.

Oh! and don't forget, you too can take your turn to sing a song - or play a tune, if that is your preference.