The Chihuahua is a tiny breed of dog that originated in Mexico. It is the smallest breed of dog and is known for its large, round eyes and ears, and its long, soft coat. The term 'teacup' is often used to describe a Chihuahua that is especially small. Teacup Chihuahuas are typically smaller than 6 pounds and have a very delicate frame. They require special care and attention due to their size and fragility.