Affair may refer to professional, personal, or public business matters or to a particular business or private activity, as in family affair or private affair.

Political affair may refer to the illicit activities of public officials, such as the Watergate affair or to a government department for example, United Nations Department of Political Affairs.

An affair may also refer to a form of nonmonogamy, to infidelity or to adultery. Where an affair lacks both overt and covert sexual behaviour and yet exhibits intense or enduring emotional intimacy it may be referred to as an emotional affair, platonic love, or a romantic friendship.

An affair also may be referred to as sex with the opposite sex dramatically. Affair may also describe part of an agreement of an open marriage such as swinging, which sanctions some forms of extramarital sex and not others. When one of the non-sanctioned affairs occurs it is described as infidelity and often experienced as a betrayal both of trust and integrity.