From Wikipedia: Senior is Latin for elder. Senior can refer to: A person of old age. The boundary between middle age and old age cannot be defined exactly because it does not have the same meaning in all societies. In many parts of the world, people are considered old because of certain changes in their activities or social roles. Examples: people may be considered old when they become grandparents, or when they begin to do less or different work — retirement. In North America and Europe, people are often considered old if they have lived a certain number of years. Many North Americans think of 65 as the beginning of old age because United States workers become eligible at this age to retire with full Social Security benefits. People in the 65-and-over age group are often called senior citizens. In 2003, the age at which a US citizen becomes eligible for full Social Security benefits began to increase gradually until it reaches 67 in 2027.