In modern usage, a blessing is thought of as a prayer, as in saying a blessing before a meal.
In the Bible and in religious contexts, a blessing, or to bless someone, takes on greater significance. Blessing someone is wishing, bestowing, bequeathing, or praying for good will, prosperity, or God’s mercy. A blessing is given to a lesser person by a greater person (Hebrews 7:7).
A secondary definition of bless is “to honor as holy” or “to glorify.” In this respect we can “bless God” or “bless the Lord.” Not all translations of the Bible use this phrasing; in this context, often praise or exalt are used instead of bless
For additional insight, consider that the opposite of bless is curse.