What is meant by taking God's name in vain? By taking God's name in vain is meant that the name of God or the holy name of Jesus Christ is used without reverence; for example, to express surprise or anger.
Blessed be the name of the Lord both now and forever. From the rising of the sun unto its going down, may the name of the Lord be praised. (Psalm 112:2-3)
Is it a sin to take God's name in vain? It is a sin to take God's name in vain; ordinarily, it is a venial sin.
Further reading: CCC 2150-2155