1) a swearing to tell the truth, the whole truth and nothing but the truth, which would subject the oath-taker to a prosecution for the crime of perjury if he/she knowingly lies in a statement either orally in a trial or deposition or in writing. traditionally, the oath concludes “so help me god,” but the approval of a supreme being is often omitted. criminal perjury charges are rare, however, since the person stating the untruth will almost always claim error, mistake, loss of memory or opinion. at the beginning of any testimony by a witness, the clerk or court reporter administers an oath to the witness. 2) the “swearing in” of a person assuming a public office, sometimes called the “oath of office.” 3) sworn commitment of allegiance, as to one’s country.