Catechism of the Catholic Church §441 — excerpt
In the Old Testament, "son of God" is a title given to the angels, the Chosen People, the children of Israel, and their kings. It signifies an adoptive sonship that establishes a relationship of particular intimacy between God and his creature.
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.