It is especially used to distinguish the Japanese popular songs from their American counterparts. The former refers to music accepted more by the young Japanese and has more musical influences from the American popular music than enka. The term enka appeared about thirty years ago to specify a more traditional and national music strongly supported by elder Japanese people.
Few teenagers listen to enka pieces.
People in their twenties who listen to enka would be considered to have very special tastes. However, the people in their forties usually are not fond of recent Japanese pop music, saying that it is noisy and childish. They, however, are strong supporters of enka. If you understand its feeling, that means you become a real Japanese adult who knows the Japanese soul.