Affordance and definition and examples: http://mohamadalmustapha.com/affordance-definition-and-examples/
Formal definition of affordance:
1. High affordance: “An object with high affordance possesses properties or features which makes it very easy and quick for any user to determine how they can use or interact with it.”
My definition: An object which can be used easily without thinking and hesitation.
2. Low affordance: Low affordance is exactly the opposite of what high affordance is. In other words, objects have low affordance when their properties do not support what intended purpose.
My definition: An object is placed at an unusual position (maybe is not visible), which is cannot be accepted by users at first.
3. Placebo affordance: An object with placebo affordance has no real function and the user is fooled by possibilities for its use which are not existent in the first place.
My definition: An object has a different appearance, which would confuses users the real function of this object.
4. Hidden affordance: A hidden affordance indicates that the object has possibilities for use, but these are not perceived by the actor.
My definition: An object has an another function and the appearance of this function is different with the main function’s exterior, which can be used as an another tool. At the same time, users need to take few minutes so that they can find out the another function.
5. Anti affordances: Anti affordances prevent or reduce interactions with a specific object.
My definition: An object reminds users not to use something which is noticed on the warning notice board. And this object trying to prevent and reduce potential dangers by noticing users.
Placebo Affordance I
Placebo Affordance II