Which term refers to an infant's reaction to their environment?

The term that best refers to an infant's reaction to their environment is temperament. Temperament encompasses the innate traits that influence how an infant reacts to the world around them. It includes aspects such as activity level, emotional reactivity, and attention span, which shape how the child interacts with their surroundings and how they respond to various situations.

While behavior, personality, and mood are related concepts, they do not specifically focus on the inherent aspects of an infant's reactions. Behavior pertains to the observable actions and responses of an individual, which can be influenced by various factors beyond innate traits. Personality develops later and encompasses a broader range of enduring characteristics that define an individual’s patterns of thoughts, feelings, and behaviors. Mood describes an emotional state at a specific time, which can fluctuate throughout the day and is not solely indicative of an infant's consistent reactions to their environment. Thus, temperament is the most accurate term to represent an infant's inherent reaction tendencies to their surroundings.