The Catechism in Questions & Answers

313. How might one take the name of God in vain?

Blasphemy is a serious abuse of the name of God, by way of which God is intentionally vilified, derided, or berated. Anyone who curses using the name of God or invokes God while telling a lie is taking the name of God in vain. Even the careless use of the names “God”, “Jesus Christ”, or “Holy Spirit” in loose talk or jokes is a violation of the Second Commandment.

In the course of history, people have frequently taken God’s name in vain in order to enrich themselves, wage wars, (e.g. the crusades), discriminate against other human beings, or to torture and kill—all in the name of God.