What is "flatteners"

Usage examples of "flatteners".

But then, when they walked along the street behind the house, the Via del Proconsolo, Edge noticed that every single shop was devoted to the display and sale of formidable canvas corsets and belly flatteners, and even uglier abdominal furniture constructed of india rubber, leather and cork—trusses, hernia belts, scrotum supporters—and he mildly suggested that the city fathers might have located Dante's presumed residence in a more high-minded neighborhood.