#3 Used unscrupulously by breeders to mislead puppy buyers.
This, unfortunately, is the most common reason for using the term teacup Maltese. And it really is a shame.
There are breeders who will advertise that they have teacup or miniature Maltese, in an attempt to sell more puppies, set high prices, or both.
They will lure in potential puppy buyers with the guise of offering special puppies that due to size are set apart from 'regular' Maltese. When in fact, they are the same size as all other Maltese that exist.
Prices for teacup Maltese may be several hundred dollars more than regular Maltese, when again, there is no difference in the size of the dog.
Reputable breeders will stand steadfast in making it clear that there is no such thing as teacups. And they will educate potential puppy buyers about these terms, usually making a statement on their site and/or once they speak to those looking for puppies.
Be wary of breeders that insist that they have a special teacup variety of Maltese dogs; this is a marketing term only.