Progressive metal (often called prog metal) is a sub-genre of heavy metal music that mixes the powerful, guitar-driven sound of metal with the complexity of progressive rock, which includes odd time signatures and complicated instrumental playing. Some progressive metal bands are also influenced by jazz fusion and classical music. Like progressive rock songs, progressive metal songs are usually much longer than other metal songs, and they are often themed in concept albums. As a result, progressive metal is rarely heard on mainstream radio and video programs.