The Yorkshire Terrier is a small dog breed of terrier type, developed in the 19th century in the county of Yorkshire, England to catch rats in clothing mills, also used for rat-baiting. The defining features of the breed are its size, 3 pounds (1.4 kg) to 7 pounds (3.2 kg), and its silky blue and tan coat. The breed is nicknamed Yorkie and is placed in the Toy Terrier section of the Terrier Group by the Fédération Cynologique Internationale and in the Toy Group or Companion Group by other kennel clubs, although all agree that the breed is a terrier. A popular companion dog, the Yorkshire Terrier has also been part of the development of other breeds, such as the Australian Silky Terrier.
--- end of quote
Info from Wiki.