What is waist training? Traditionally "waist training" referred to the use of steel boned corsets to develop an exaggerated hourglass shape. By cinching a corset tighter and tighter, the waist trainer corset was able to pull in a woman's floating ribs and even do a bit of rearranging of her internal organs to effectively reduce the circumference of her waist. The effect is semi-permanent, requiring continued corseting even after the goal reduction has been achieved.
More recently, celebrities like Kim Kardashian and Amber Rose have redefined the term with the use of latex waist cinchers during workouts, shifting the entire concept of waist training (we refer to this practice as "waist taming"). Women discussing "waist training" these days are, more often than not, likely discussing it as a part of their workout plan.