1. a temporary readiness to respond in a certain way to a specific situation or stimulus. For example, a sprinter gets set to run once the starting gun fires (a motor set); a parent is set to hear his or her baby cry from the next room (a perceptual set); and a poker player is set to use a tactic that has been successful in other games (a mental set). See also preparatory set.

2. a collection of psychological factors (expectations, beliefs, mood, etc.) that can influence an individual’s response to a drug.

3. in mathematics and logic, a collection of entities that is itself regarded as an entity. A set that is defined by a condition, such that its members must possess a particular attribute or attributes, is known as a class.