Tea Cup is a size reference in Dogs. It means the Dog is so small it will fit in a tea cup. Many Dogs will only fit in the tea cup while puppy's though.
Teacup dogs are tiny size versions of regular dogs. They usually are more pricey and harder to find at times. A teacup dog is usually about a fourth of the size of a regular sized dog and they usually weigh 1-2 pounds and sometimes less.
Teacup dogs are very small breeds of dogs, or smaller versions of already small breeds of dogs. For example, wiener dogs come in two sizes: standard and mini. A teacup size would be an even smaller version of the mini.
Teacup dogs are a smaller form of a dog. There is a normal size, then there are miniature dogs, then there are Teacups. Literally the size of a teacup. Very cute and VERY small!
There is no such thing as a "teacup" dog. Teacup is a term used by breeders to describe very small dogs, when in fact they are usually premature or unhealthy.