Catechism of the Catholic Church §2508 — excerpt
Lying consists in saying what is false with the intention of deceiving the neighbor who has the right to the truth.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.