Using the term teacup or toy is not to make more money off people. Its so you know the size of the puppy. Certain people like smaller dogs, its not a big deal or a bad thing like these people are saying. Calling a dog teacup or toy is not to scam people out of money. My dogs are both about 4 pounds each and the female already had her pups, I described them as teacup chihuahuas. And evidently I wasn't doing that to try to make money because I gave them away for free!!
There is really no such thing as a Teacup Chihuahua! There are only two types of Chihuahuas and that is the Short Coat and the Long Coat. The Teacup term is just a name, that some breeders use, in order to charge more for their puppies. The reason they are called Teacups is because a runt is bred with another runt, to produce smaller puppies. Runts need to be watched very carefully, because some of them are prone to some serious health problems. That does not mean all of them are! I have seen runts grow bigger, than their siblings are!
Remember that the Kennel Clubs have developed breed standards for each recognized breed of dog. These standards are guidelines for breeding healthy, genetically sound animals. Chihuahuas should weigh less than six pounds but it's the overall build of the dog which is most important. You should be shopping with reputable breeders who are trying to breed high quality dogs that meet the breed standards - of size and all others. Anyone who advertises so-called "Teacup" animals is implying that their dogs are smaller than "normal." Any breed which is consistently bred for a particular trait (such as small size or an unusual color, etc.) will usually result in inferior animals (genetically) which then results in the illnesses and conditions described by the previous answer.
Remember that "Teacup" means smaller than normal and is usually a sign of a breeder who is more interested in making money than in breeding healthy, long-lived dogs. Also remember that Chihuahuas are all very small and fragile It's hard to predict how large or small an adult Chihuahua will actually be so why not look up a Chihuahua rescue organization and adopt an adult pet? Google "Chihuahua Rescue" and you'll find ads with photos and the rescue fees are much less than the cost of a puppy.
I agree that a Teacup is just the runt of the litter. But I'll also answer your question.
A teacup is a term used for a Chi under 4lb.
There is no particular difference between toy Chihuahua and tea cup puppy. People often use the term tea cup for this breed of dogs to make it sound more attractive. You should be careful about its health. It is vulnerable in following ways:
Its bones are vulnerable to diseases
Its joints and muscles sometimes get affected
Its ears eyes teeth and mouth should be regularly observed
It gets diseases which affect its digestive tract, and respiratory system
Its reproductory and urnary system should also be taken care
It sometimes gets Patellar Luxation and Entropian
Good luck and take care of your new fellow
So is there toy chihuahua? Or just different sizes? And there is no way to tell?