Affordances

"term that refers to the properties of objects -- what sorts of operations and manipulations can be done to a particular object" (D. A. Norman 1988, The Psychology of everyday things).

A door affords opening
A chair affords support

"perceived affordance": the extent to which interface objects suggest their affordance.

2nd revised edition 2013: Signifiers indicate the affordance of an interface object. They need to be carefully designed to be able to do this.

The image shows the affordances
of door handles and scroll bars. The perceived performance of
some elements is better than that of other elements.

User interface elements should be designed in such a way that they clearly indicate their affordances.