In Japanese dramas, people always pray before eating, and then what does that mean?

Japanese people are very polite, of course, you can also say that this is a gift.

That Japanese sentence is: ぃただきます! (The Roman word is i ta da ki Ma Su), which means "I received it". There is an element of gratitude in semantics. You must say it before eating. This is a courtesy and a thank you for having a meal. It may also be translated into "I'm starting" or "I'm going to start eating" in TV series.