Rav is a variant of Rebbe according to this wiki page
Rebbe (רבי) (pronounced /ˈrɛbə/ in English[1]), which means master, teacher, or mentor, is a Yiddish word derived from the identical Hebrew word Rabbi. It mostly refers to the leader of a Hasidic Jewish movement. In accordance with Yiddish pronunciation norms, the stress is on the first syllable and the final vowel is sometimes reduced to a schwa.