An affordance signifies what action is possible. It is the relationship between the properties of an objects and the capabilities of the user that determine how the object could be used. For example, a chair affords (“is for”) support and therefore affords sitting. If an affordance or anti-affordance cannot be perceived, some means of signaling its presence is required.
An object’s affordances are never equally perceptible to all, and never equally available to all.
See: Design Justice