A cross lace decoration in the center of the waist area to make it more form fitting, a very classic "corset" appearance.
This includes both ones on a real Corset and ones attached to a Skirt or Dress, but the cross lace part should stay "corset-like". If it expands upwards or downwards, it's a Cross-Laced Top, Cross-Laced Skirt or Cross-Laced Dress instead, depending on the type of clothing item.