This character wears a baby-doll.

A babydoll is a short, sometimes sleeveless, loose fitting nightgown or negligee intended as nightwear for women. It sometimes has formed cups called a bralette for cleavage with an attached loose fitting skirt falling in length usually between the upper thigh and the belly button. The garment is often trimmed with lace, ruffles, appliques, marabou fur, bows and ribbons, optionally with spaghetti straps. Sometimes it is made of sheer or translucent fabric like nylon or chiffon or silk.

NSFW Comparison - Left: chemise, center: teddy, right: baby-doll. Only the teddy wraps around the crotch, and the baby-doll is much looser around the hips than the chemise.