High Quality Content by WIKIPEDIA articles! Perjury, also known as forswearing, is the willful act of swearing a false oath or affirmation to tell the truth, whether spoken or in writing, concerning matters material to a judicial proceeding. That is, the witness falsely promises to tell the truth about matters which affect the outcome of the case. For example, it is not considered perjury to lie about one`s age unless age is a factor in determining the legal result, such as eligibility for old age retirement benefits.