Affordance   A use that an object can be put to. This may be intentionally designed in or be entirely coincidental. e.g Fire extinguishers afford you the possibility of spraying fire controlling substances, they are also 'misused' as door stops all over the world. Flat head screwdrivers afford you the ability to drive screws into wood, they also exercise your wrist and grip, but can also be misused in opening tins of paint

Signifier   Any feature of an object that lets you know how to interact with it.

• Primary signifiers are aspects that by their very shape and nature let you know what to do with it. For instance handles whose forms invite you to hold, turn and pull.
• Secondary signifiers are signs, symbols, and labels on the object which give additional information when the form of the object does not make it entirely clear. (Arrows/Play/Pause sign or words/On/Off/No step etc) (see also : Mapping)