Fecal scented air expelled through the anal cavity. You must not be fooled by its pretty-sounding name, as "The Dirty Wind" is one of the most sought after farts. It is comforting to farter and passerby alike. It has a sound of air being let out of a bike tire ffffffffffffffft. What is most diagnostic about it, however, is its length. It is the longest-lasting fart there is. It will sometimes cause the farters mouth to hang open uncontrollably with eyes watering & unable to speak. It's as though he has had the wind knocked out of him. Neither loud nor strong in sound this fart however is unwavering, it may last fifteen seconds.
Derek was hiking near his home when he suddenly stopped dead in his tracks... he felt the presence of a Dirty Wind approaching and thus slightly bent over at the waist, hands on hips as he released his dirty wind for the other hikers to appreciate.