Reb (Yiddish: רעב) is a Yiddish honorific traditionally used for Orthodox Jewish men. It is not a rabbinic title; it is the equivalent of the English "mister". In writing it is abbreviated as 'ר.
The title was adopted by Orthodox Jews at the time of the schism with the Karaites, as a sign of loyalty to Rabbinic Judaism.[1]
When addressing someone directly, Reb is usually used with the first name only ("May I help you, Reb Chaim?"). In other circumstances, it can be used with either the first name or the full name ("This is Reb Chaim Jacobs."; "Would you please help Reb Chaim?"). In formal written address, it is usually used along with the full name. It is never used with the surname alone.[2]
When a man's name is unknown, he is often addressed as Reb Yid ("Mr Jew").