There isn't any such thing. The terms such as teacup, pocket, micro and whatever else they come up with next do not actually exist as classifications. If you have a 2 pound chihuahua you have a two pound chihuahua, if you have a 12 pound chihuahua you have a 12 pound chihuahua (or yorkie, or Maltese or whatever else for that matter).
The problem (or A problem) with buying a puppy from someone who uses those terms to describe their puppies (and in some breeds like the bulldog it is mini) is that they are probably either dishonest or they are not knowledgeable enough about their breed (and possibly breeding though they may have good intentions) if they don't even know that's a made up sales tactic. Both scenarios can contribute to an unhealthy puppy and neither of those is likely to be able or willing to properly educate you on the negatives, risks, and additional care that the really tiny ones need. While a breeder may have smaller dogs the ones you want to buy from NEVER use those terms and will adamantly tell you they don't exist while explaining the extra care, health problems, and usually shorter life span of their pup that is likely to be much smaller than the average (among other distinctions).
Here's what some of the breed clubs (who determine and set the AKC standard which means the IDEAL example of that breed here in the USA have to say about those terms:
Chihuahua: www.chihuahuaclubofamerica.com
Shih-Tzu: www.americanshihtzuclub.org
Yorkshire terrier (yorkie): www.ytca.org (They have just added some definitive DQ's concerning color I believe as well)
Maltese: At the bottom of the page under Maltese Myths www.americanmaltese.org
Poodle: www.poodleclubofamerica.com
The problem (or A problem) with buying a puppy from someone who uses those terms to describe their puppies (and in some breeds like the bulldog it is mini) is that they are probably either dishonest or they are not knowledgeable enough about their breed (and possibly breeding though they may have good intentions) if they don't even know that's a made up sales tactic. Both scenarios can contribute to an unhealthy puppy and neither of those is likely to be able or willing to properly educate you on the negatives, risks, and additional care that the really tiny ones need. While a breeder may have smaller dogs the ones you want to buy from NEVER use those terms and will adamantly tell you they don't exist while explaining the extra care, health problems, and usually shorter life span of their pup that is likely to be much smaller than the average (among other distinctions).
Here's what some of the breed clubs (who determine and set the AKC standard which means the IDEAL example of that breed here in the USA have to say about those terms:
Chihuahua: www.chihuahuaclubofamerica.com
Shih-Tzu: www.americanshihtzuclub.org
Yorkshire terrier (yorkie): www.ytca.org (They have just added some definitive DQ's concerning color I believe as well)
Maltese: At the bottom of the page under Maltese Myths www.americanmaltese.org
Poodle: www.poodleclubofamerica.com