Pequin is a capsicum annuum variety that is grown in the wild in Northen Mexico and part of Southern United States.  It is cousin the the Chiltepin pepper and many have confused these to be the same variety.  I have grown both varieties and the most noticeable trait that distinguish them apart is the shape of the fruits.  Chiltepins are round, pea-shaped and the Pequin are more of an oval shape.  Depending on condition and grow space, Pequin peppers can grow massive in size, easily reaching 5 feet and produce a ton of tiny size pods.  A very common name for this pepper is "Bird Pepper" as the birds love eating them and are unaffected by capsaisin.  The flavor of this pepper is described as being very hot, slightly fruity with some smokiness.

Common uses for this pepper is powder, hot sauce or pickled.  Cholula is one fo the more popular hot suace for this pepper.