What does "perjury" mean?

Perjury: (Law) At common law, a willfully false statement in a fact material to the issue, made by a witness under oath in a competent judicial proceeding. By statute the penalties of perjury are imposed on the making of willfully false affirmations. Note: If a man swear falsely in nonjudicial affidavits, it is made perjury by statute in some jurisdictions in the United States.