Echos

Echos is the name in Byzantine music theory for a mode within the eight-mode system (oktoechos), each of them ruling several melody types, and it is used in the melodic and rhythmic composition of Byzantine chant, differentiated according to the chant genre and according to the performance style. It is akin to a Western medieval tonus, an Andalusian tab', an Arab naġam, or a Persian parde.