The maximum Waist reduction that a garment is rated to. Your Corset may go further than this but we don’t recommend it. Remeber you don’t have to wear corsets as tightly as they will go.
How easy is a corset to disguise underneath clothing. Even garments which score a 10/10 here may give up a little silhouette underneath very sheer or body hugging clothing.
How comfortable a design is to wear for long periods of time. If a corset has a low score here it may be extremely comfortable for short periods of wear, but could be a less “breathable” fabric so not suitable for long periods.