Personality refers to qualities of a person's character that make them unique. Psychologists view personality as a dynamic concept describing a person's whole psychological system and growth over time. Gordon Allport defined personality as the dynamic organization within an individual that determines their unique adjustments to their environment. The Big Five personality model identifies five key dimensions that make up an individual's overall personality: extraversion, agreeableness, conscientiousness, emotional stability, and openness to experience. These dimensions are often used by human resources professionals to help place employees.