Hallelujah is a word we use to say "Praise the Lord!" It is often used in religious songs and prayers as a way to express joy and gratitude. When we say "hallelujah," we are thanking God and showing our appreciation for all the good things in our lives. It's like saying "yay, God!" or "thank you, God!" So, whenever you hear someone say "hallelujah," you can know that they are very happy and thankful for something that God has done for them.