Reb is a Yiddish word that is used to show respect to someone who is older or wiser than you. It's kind of like saying "mister" or "sir" in English. It's also used as a title of respect for someone who is a religious leader, like a rabbi. When you say "Reb," it's a way of showing that you think this person is very special and important, and you want to show them respect. It's like saying "this person is really cool and I want to be their friend."