Babydoll or Empire waist?
Empire Waist Dress according to about.com:
A type of dress or top where the waist line is raised above the natural waistline, sometimes as high as right below the bust. Best on slender-on-top or petite figures, the empire dress creates the illusion of length and camouflages a bottom-heavy figure or thick waist (above from Lux UO).
A babydoll is a short nightgown or negligee intended as nighwear for a female. The garment is often trimmed with lace, ruffles, bows and ribbons, optionally with spaghetti straps. Short daywear dresses of a similar style are sometimes called babydoll dresses. Some styles are similar to what is worn by dolls in the form of infants, and by some infants; the gown is short enough that diapers are easily changed (above from Anthropologie).
To be honest, I'm not too sure about apparel search's definition of the babydoll dress. It makes it sound like some kind of erotic dress when its just really cute. But here you go. Basically, Baby doll dress is a shorter type of empire waist dress.