What is a "Designer" dog or for our purpose a "Designer" Shih Tzu?
Wikipedia states "The terms crossbreed, mongrel, mutt and designer dog all refer to the intentionally bred
offspring of two or more different recognized dog breeds."
So in the case of the Shih Tzu it would mean that a purebred Shih Tzu was intentionally bred with another breed to such as a Poodle to produce the "Pooshih" or Shihpoo". Some breeders say they breed the two breeds to achieve the best attributes of both breeds. Other breeders do so without the intentions of making a better breed but to use the "designer" term to charge more for their puppies. These breeders usually breed two breeds without regard to characteristics in order to come up with a cute title such as "Labradoodle", "Pooshih", "Puggle", etc.
For more information about the "Designer" dog go to the American Shih Tzu Club's page