Progressive rock is a genre that was far more popular in the seventies and eighties than it is now, with bands like Yes, Asia, King Crimson, some Genesis, Pink Floyd, and so on. The key characteristic is that most songs are fairly complex in terms of musical themes and composition, often also rather longer than normal rock songs, with some cases of songs lasting twenty minutes and more (such as Yes' legendary Close to the Edge). There are often long instrumental sections without lyrics, and the lyrics that are there are often poetic and abstract (detractors might also say they can be pompous and sometimes make little sense; some of the lyrics of Close to the Edge are indeed puzzling to say the least).

(Heavy) metal is somewhat similar to the extent that it also has longer than average songs, long instrumental sections and an inclination towards the dramatic and pompous in the lyrics, often with themes of death, violence, war or horror. The difference is in the instruments used and the general sound, as the name indicates heavy metal relies more on heavier instruments, mostly electric guitar and bass. Famous bands include Iron Maiden, Metallica, Black Sabbath, and the like. There are many subgenres with their own particular characteristics, some of them in rather questionable taste (such as the appropriately named band Cradle of Filth) which sometimes makes people think badly of metal as a whole.

So progressive metal is the subgenre of metal that leans the most in the direction of progressive rock, with a somewhat softer sound, a preference for good and elaborate compositions over simple guitar riffs, and lyrical themes that stay far away from the death-and-satanism tropes of certain other metal bands.