1/3 Kid
Dolls in this size are kid-shaped, but about the same height as a bunch of 1/4 scale adult dolls. Because of this they are often categorized as 1/4, but they're really 1/3--just kid 1/3!
Dolls that can be clothed with patterns in this size are slightly thicker in the torso/limbs and have a less dramatic bust:waist:hip ratio than Slim MSD. Examples of this size are Volks MDD Mini Dollfie Dream/MSD and Obitsu's 40cm dolls.
If you have a doll in this size with a large bust (like a MDD with a large bust), you'll do better in the 1/4 Slim MSD pattern size printing at 107% and using the wide chest/waist cuts.