Catechism of the Catholic Church §1751 — excerpt
The object chosen is a good toward which the will deliberately directs itself. It is the matter of a human act. the object chosen morally specifies the act of the will, insofar as reason recognizes and judges it to be or not to be in conformity with the true good.
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.