Presto,
That's true, it's just a cute name that refers to those who are under 4 lbs.
But there is no official separate Yorkshire "breed" which is recognized as a
TeaCup.
Also, you'll hear the term "Toy Yorkie"... which is also misleading,
OF COURSE Yorkies are Toys. That's their official category.
There are Breeders, who select pairs based on what size pups they throw,
and intentionally "create" a situation where the offspring size is reduced.
This activity usually creates some serious problems in the animals,
and most here will tell you is wrong to do that.
HA, we also use "TeaPot", referring to those who are over 7.1 lbs.