Sentence:  <WSD>Affordances</WSD> provide strong clues to the operations of things. Plates are for pushing. Knobs are for turning. Slots are for inserting things into. Balls are for throwing or bouncing. When <WSD>affordances</WSD> are taken advantage of, the user knows what to do by just looking: no pictures, label, or instruction is required. 
Meaning of the word marked with <WSD> tags:  Any interactive control or component serving as a cue to the user to take some action.