It's a type of rock music defined by a heavier sound that can vary quite a bit. It certainly doesn't require a harsh sonic structure and shouted or screamed vocals make up a minority of the vocalizations of traditional heavy metal forms.
Despite your earlier attempts to claim something to the contrary, Black Sabbath were one of the first bands to be labeled as heavy metal, as early as 1971. They don't sound like the description that you gave. Neither do the early albums of Judas Priest, which are undeniably heavy metal. Similarly, a lot of other early heavy metal bands don't really match that description.