An attestation by a person which binds him or her legally and morally. Usually attesting to the truth of something, as an affidavit, or the validity of one's signature. A promise to tell the truth. Also, a promise to carry out a duty with high morality (oath of office). An oath has religious connotations and usually involves the word "swear", and may contain the phrase "so help me God", or require the one taking the oath to put his or her hand on a bible. An affirmation (see which) is still legally binding.