I`d say an iconic bass-line would mean that a song is instantly recognisable by it, from a majority. As above Another One Bites The Dust is a great example, even if people don`t know the name of the song or the artist if they recognise the song from the bass then to me it`s there. Billie Jean for me is another like this (though not sure how many people wouldn`t know it was Michael Jackson).