In legal definitions for interpersonal status, a single person is someone who is not in a relationship or is "unmarried".
In common usage, the term single is often used to refer to someone who is not involved in any type of serious romantic relationship, including long-term dating, engagement, or marriage. Both single and unmarried people may participate in dating rituals and other activities to find a long-term partner or spouse. However, in some cases single people are not interested in marriage, domestic partnership, or other types of formal, committed relationships.
People may remain single for a variety of reasons, including financial and emotional or physical health issues, stress in the family, time constraints, education, career, personal preferences, advanced age or social fears, and living in a society or locality where there are an insufficient number of people of the preferred sex for romantic or sexual attraction.