Horrible music that the general population likes. Ass Rock is typically 70's and 80's rock music that mysteriously became popular despite how bad the song actually is.
Example 1
Guy 1: The song "pour some sugar on me" by def leppard is the best song EVER!
Guy 2: No it's not, they lyrics don't make sense, it's such an ass rock song.
it's exactly what it sounds like, a rock that smells asthough it has been thoroughly, and deeply covered in shit. There is usually no context as to how the rock smells this way, but it happens. Apparently this happens in Australia alot too, ass rocks are just regular rocks found along the ground.