An affordance is often taken as a relation between an object, or an environment, and an organism that affords the opportunity for that organism to perform an action. For example, a knob affords twisting, and perhaps pushing, while a cord affords pulling. As a relation, an affordance exhibits the possibility of some action, and is not a property of either an organism or its environment alone.Different definitions of the term have developed. The original definition described all actions that are physically possible. This was later adapted to describe action possibilities of which an actor is aware. Some define affordance as a potential resource for some (not a particular) organism or species of organism, and so while inviting the possible engagement of some species, not identified with any particular one. The term has further evolved for use in the context of human–computer interaction (HCI) to indicate the easy discoverability of possible actions.The word is used in a variety of fields: perceptual psychology, cognitive psychology, environmental psychology, industrial design, human–computer interaction, interaction design, instructional design, science, technology and society (STS), and artificial intelligence.