The definition of what is and isn’t folk has changed radically. It used to be confined to songs of which the composer isn’t known. But in fact some “folk” songs turn out to be Victorian parlor ballads (“Wildwood Flower”) or minstrel songs (“Oh, Susannah”). Then there are the folklike or honorary folk songs, such as “Dona, Dona” (Yiddish musical theatre), “They Call the Wind Mariah” (musical), anything by Woody Guthrie, various singer/songwriter songs. Actually, some people call it a folk song as long as it’s played on acoustic instruments, I’ll be danged if I understand why.