Bey (Ottoman Turkish: بك, Beg, Beğ) is a title for chieftain, traditionally applied to the leaders of small tribal groups. According to some sources, the word "Bey" is of Turkish language In historical accounts, many Turkish, other Turkic and Persian leaders are titled Baig|'Bey, Beg, Bek, "Bai" Bay, "Baj", Baig or Beigh. They are all the same word with the simple meaning of "lord". The regions or provinces where beys ruled or which they administered were called beylik, roughly meaning "emirate" or "principality" in the first case, "province" or "governorate" in the second (the equivalent of duchy in Europe).

Today, the word is still used informally as a social title for men (somewhat like the English word "mister"). Unlike "mister" however, it follows the name and is used generally with first names and not with last names.

Read more about Bey:  Turkish and Azerbaijani Beys, Beys Elsewhere, Etymology