This is a close cousin to the corset and sometimes even online shops use the terms interchangeably, but it’s definitely its own thing. Bustiers have, well… “boost”! Where corsets are typically flat across the front, a bustier has cups to hold the girls – more like an elongated bra with the body of a corset (though often a less rigid body, letting you breathe without shifting your internal organs).
They can be slightly shorter than corsets and are typically fitted close to the body, so it’s important to make sure they hug your curves without cutting in. Sometimes they’ll come with a matching pair of panties, but my general rule is to ditch those and find a nice pair of booty-hugging lace panties instead.