Categorization is a universal psychological process involving the creation of groups of objects, people, or entities, based on common characteristics. Even when stimuli differ from one another in gradual ways (e.g., along a continuum), people naturally tend to divide them into categories. Although some categories (e.g., colors, emotional expressions, geometric shapes), like the process of categorization, may be universal, the way people group many other things differs across cultures. Categories may include such groupings as stereotypes (categorizing people based on perceived common characteristics) or concepts (categorizing objects based on common attributes).