Answer:
Yes and no; teacup dogs are actually undersized toy dogs. This name is only a marketing technique used by kennels and puppy mills to increase dog sales by creating the impression that the "teacup" dogs are cuter and more valuable than toy dogs. Actually, they're the product of runts.
As a result, teacup dogs usually have many health problems and a shorter life span. Their bones are also very fragile and can be damaged easily.
Teacup dogs are not approved by reputable kennel clubs including the Kennel Club (KC), the American Kennel Club (AKC) and the Continental Kennel Club (CKC). Teacups are not considered as a separate breed in any way or form. Besides, teacup dogs do not fit the breed standards of toy dogs since they are undersized.