Perceived affordance is the quality of an object that suggests how it might be used.
In screen-based communications, the concept of perceived affordance is useful when designing or evaluating a graphical user interface (GUI). To quote user-engineering proponent Don Norman:
Does the user perceive that clicking on that object is a meaningful, useful action, with a known outcome? 
Affordance is a term created by the perceptual psychologist J. J. Gibson to refer to the qualities of the physical world that suggest the possibility of interaction relative to the ability of an actor (person or animal) to interact. McGrenere and Ho presented three fundamental properties of an affordance as defined by Gibson:
For example, the affordance of a branch as ‘a nice place to sit’ are dependent on:
Based on the original definition and fundamental properties, affordance, in relation to interface design, relates more to (physical) input devices: mouse, keyboard, stylus, etc. When discussing the qualities of a graphical user interface, the preferred term is perceived affordance.
User-engineering proponent Don Norman used the term affordance in the context of product design, and how the design of an object suggests its use.
When you first see something you have never seen before, how do you know what to do? The answer, I decided, was that the required information was in the world: the appearance of the device could provide the critical clues required for its proper operation. 
At this point the term affordance was introduced to the graphical and industrial-design communities. Subsequently Norman has sought to distinguish between the actual (natural, physical) properties of an object and the appearance of affordance by adding the qualifier ‘perceived’.
The designer cares more about what actions the user perceives to be possible than what is true. (emphasis added) 
This is what the interface designer should care about: Does the user perceive that clicking on that object is a meaningful, useful action, with a known outcome? (emphasis added) 
The perceived affordance an object (or interface element) is determined by factors including:
For example, in the context of a website, the perceived affordance of underlined text is that it indicates a hyperlink; and, that when followed (clicked), the user will link to information that relates to the hyperlinked word or phrase.