Bayātī (Arabic بياتي; Turkish Beyâtî), also known as Bayat and Uşşâk (Ushaq), is the name of a maqam (musical mode) in Arabic, Turkish, and related systems of music.
Bayati is similar to a natural minor scale, with the primary exception of a half-flat second degree.
Syrian Jews have an abundance of pizmonim in this maqam and usually apply it to all Bar Mitzvahs and to Saturday Night services.
A general rule: they tend to be less flat while playing an ascending phrase and vice versa.
In Turkish Ottoman music, the Beyati quartertone is generally played slightly less flat than the ‘darker’ Ussak tone.