Ageism refers to prejudice and prejudicial treatment against people older than a certain age (usually in the mid-50s). In U.S. society, the elderly tend to be less and less visible in mainstream activities, in organizations, and in the workplace. One theory assigns this to ageism. Is ageism the best explanation for this phenomenon? If yes, why is this so? If not, what would be the best alternative explanation? What is the most common expression of ageism?