Abortion is the direct killing of an innocent human being and is a violation of that person’s right to life.
From the Catechism of the Catholic Church: 2271 Since the first century the Church has affirmed the moral evil of every procured abortion. This teaching has not changed and remains unchangeable. Direct abortion, that is to say, abortion willed either as an end or a means, is gravely contrary to the moral law:
You shall not kill the embryo by abortion and shall not cause the newborn to perish.75
God, the Lord of life, has entrusted to men the noble mission of safeguarding life, and men must carry it out in a manner worthy of themselves. Life must be protected with the utmost care from the moment of conception: abortion and infanticide are abominable crimes.76
75 Didache 2,2:SCh 248,148; cf. Ep. Barnabae 19,5:PG 2 777; Ad Diognetum 5,6:PG 2,1173; Tertullian, Apol. 9:PL 1,319-320.
76 Gaudium et Spes 51 § 3.