Plural form of the Hebrew word "mitzvah" which means "commandment," it has two meanings. The first are the commandments given in the Torah. ("You should obey the mitzvah of honoring your parents!") The second is a good deed. ("Helping her carry her groceries home was such a mitzvah!")
Hebrew for "my master," the term refers to a spiritual leader and teacher of Torah. Often, but not always, a rabbi is the leader of a synagogue congregation.