As far as I know 'teacup' poodles is just a term they use to describe the dog. Same thing as the 'teacup' yorkies out there now 
The poodles I know of are standard; mini & toy size... This is what I got from the AKC website:
Size, Proportion, Substance
Size
The Standard Poodle is over 15 inches at the highest point of the shoulders. Any Poodle which is 15 inches or less in height shall be disqualified from competition as a Standard Poodle.
The Miniature Poodle is 15 inches or under at the highest point of the shoulders, with a minimum height in excess of 10 inches. Any Poodle which is over 15 inches or is 10 inches or less at the highest point of the shoulders shall be disqualified from competition as a Miniature Poodle.
The Toy Poodle is 10 inches or under at the highest point of the shoulders. Any Poodle which is more than 10 inches at the highest point of the shoulders shall be disqualified from competition as a Toy Poodle.