Hebrew words of celebration.
Mazel tov (also spelled mazal tov, or mazel tof) are Hebrew words that literally translated mean "good luck." In practice, mazel tov is usually said to mean "Congratulations!"
One can expect to hear people shout mazel tov at Jewish weddings just after the groom breaks the glass, at brit milah (bris) ceremonies, and at bar/bat mitzvahs. Mazel tov is an appropriate response to any good news, from an engagement to a graduation, a new job, a new house, or any other honor or milestone.
Some people avoid saying mazel tov to a pregnant woman out of superstition that something might happen to the baby. Instead, it is customary to say "b'sha'ah tovah," meaning "at a good time." The implicit wish is that the baby will be born healthy and safe--at which point mazel tov would be an appropriate greeting.