A Onepiece (also called an OP) is a Lolita dress with short, detachable or long sleeves. It is perfect in all seasons thanks to its wide range of materials: cotton, polyester, or even wool.
It is not necessary to wear a Blouse or a Cutsew underneath, which makes it easier to coordinate.
It is often appreciated for its intricate details, sometimes very Princess like (embroidery, bows, ruffles, pearls, laces, etc.)
A Onepiece is a Lolita dress with long, short or detachable sleeves.
A Jumperskirt is a sleeveless Lolita dress, with jumpers, where you can wear a Blouse underneath.
The possibilities are infinite with your Onepiece. A Petticoat will add volume, Bloomers or Drawers can add a cute touch to your outfit. A head accessory like a matching Headdress as well as Jewels will enhance your Lolita outfit.
A Onepiece is a Lolita dress that is very easy to wear because you do not need a Blouse underneath. It is very easy to coordinate and match.
But it is possible to add a Blouse, a Cutsew or even a Pullover underneath a Onepiece with short sleeves, or on top of a Onepiece with long sleeves: it allows a lot of versatility.