A bustier is a piece of clothing that girls and women wear to make their chest look bigger and flatter their tummy. It's like a fancy bra that also covers your tummy and waist! It's made of stretchy fabric, hooks or buttons at the front, and often has straps that go over your shoulders.
When you wear a bustier, it can make your chest look a little bit like you have more there than you really do because it has special cups that push your chest up and make it look fuller. It also helps smooth out your tummy, so it looks flatter and more toned.
Bustiers are often worn under fancy dresses or outfits for special occasions, like weddings or prom. They can come in lots of different colors and designs, so you can pick one that matches your outfit perfectly!