Bey is the Turkish word for "chieftain". In historical accounts, many Turkish and Persian leaders are betitled bey, beg or beigh. They are all the same word with the simple meaning of "leader".
Note that the first three rulers of the Ottoman Empire were entiled bey and not sultan which came in use first after 1383.
This title was used also in Albania (Albanian language: bej, be, or beu) which used to be under the Ottoman Empire. Although originally it was associated only with people to whom the title was given by Turkish officials, it was later used on/by wealthy landlords even after Albania's independence in 1912. This term is not used anymore except when referring to historical figures, events or for humorous purposes.