Technical death metal and progressive death metal are related terms that refer to bands particularly distinguished by the complexity of their music. Common traits are abruptly changing, sometimes chaotic song structures, uncommon time signatures, atypical rhythms and unusual harmonies and melodies. Bands described as technical death metal or progressive death metal usually fuse common death metal aesthetics with elements of progressive rock, jazz and/or classical music. While the term technical death metal is sometimes used to describe bands that not only focus on complexity but also on speed and extremity, the line between progressive and technical death metal is thin. "Tech death" and "prog death", for short, are terms commonly applied to such bands as Cryptopsy, Edge of Sanity, Opeth, Origin and Sadist. Cynic, Atheist, Pestilence, Disharmonic Orchestra and Gorguts are examples of bands noted for creating jazz-influenced death metal. Necrophagist and Spawn of Possession are known for a classical music influenced death metal style. Death metal pioneers Death also refined their style in a more progressive direction in their final years. .