Wikipedia
The zortziko is a dance rhythm that originates in the Basque Country. It is also used as an accompaniment rhythm for vocal melodies, such as " Gernikako arbola", the unofficial anthem of the Basques, composed in 1853 by José María Iparraguirre .
The zortziko has a distinctive 5/8 time signature, consisting of three subdivisions of 1, 2, and 2 beats. Some theories hold that it is in 5/4 time, "like the Rueda except that the 2nd and 4th beats are almost always dotted notes" , or that it actually a double compound meter combining an irregular binary (5/16 divided 2 + 3) and an irregular ternary (8/16 divided 2 + 3 + 3), creating an ostinato pattern of "irregular bichrome" measures, which in Constantin Brăiloiu's terminology is called an aksak rhythm .
Despite the zortziko's origins and continued popularity in folk music, some composers (including Isaac Albéniz, Charles-Valentin Alkan, Aita Donostia, Jesús Guridi, Gabriel Pierné, Maurice Ravel (in his piano trio), Pablo de Sarasate, Pablo Sorozábal, and José María Usandizaga ) have also incorporated it into classical music. British composer Michael Finnissy used the zortziko rhythm as the basis for his 2009 orchestral piece Zortziko, commissioned by the Basque National Orchestra.