Mazel tov!

It's some kind of celebration in the Jewish religion, but I can't tell you exactly what it means, sorry...

It's Hebrew for best wishes or congratulations.

Vorpar's answer is correct! It's a Jiddish expression and means "Good luck!"

Ah! So it's what you say at a celebration, and not the celebration itself? Thanks, Vorpar!

Yes - literally it means "good luck" or "good fortune," but it is used more like "congratulations." In other words, you don't say it to wish someone good luck, but to congratulate them on something that has already happened. ("I hear your daughter got engaged. Mazel tov!" -- not "I hear you need open-heart surgery -- mazel tov!" )

Thank you all. I got it. And it's kinda like "well done!" too, right?

And I guess I'll never forget it because of this wonderful example.

Yes, it can also be used to mean "Well done!"

Glad you like my example!