Catechism of the Catholic Church §1951 — excerpt
Law is a rule of conduct enacted by competent authority for the sake of the common good. the moral law presupposes the rational order, established among creatures for their good and to serve their final end, by the power, wisdom, and goodness of the Creator.
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.
Also cites: Leo XIII, Libertas praestantissimum: AAS 20 (1887/88), 597 · St. Thomas Aquinas, STh I-II, 90, 1 · Tertullian, Adv. Marc, 2, 4: PL 2, 288-289