"Teacup" and "Deer-faced" Chihuahuas
Along with "mini," "pocket" and "tiny toy", "teacup" is sometimes used to describe Chihuahuas and other dogs that are very small. These and similar terms are not officially used by any kennel club or reputable breeder, and are not breeds or specific types of Chihuahua. In particular, all Chihuahuas are toy dogs; there is no such thing as a "toy Chihuahua."
Some potential buyers seek extremely small animals; very small dogs, however, are often runts. They are often unhealthy, or undernourished, or, if otherwise healthy, may suffer shortened life spans and health problems later in life due to extreme dwarfing. They are not normally suitable for breeding, and require special care. Some breeders of Chihuahuas purposely attempt to breed very small animals, and increase the prices of the smallest dogs, or specifically advertise tiny animals. Reputable breeders disapprove of such practices, pointing out that it is difficult to predict the adult size of a given puppy, and citing the other issues discussed above.
http://en.wikipedia.org/wiki/Chihuahua_(dog)