Cengkok are patterns played by the elaborating instruments in the Javanese gamelan

Gamelan

A gamelan is a musical ensemble from Indonesia, typically from the islands of Bali or Java, featuring a variety of instruments such as metallophones, xylophones, drums and gongs; bamboo flutes, bowed and plucked strings. Vocalists may also be included....

. Typically they are melodic patterns that lead to the seleh

Seleh

The seleh note or nada seleh is a concept used in Javanese gamelan music. It is the final note of a gatra, or four-beat melodic unit.The main underlying melodic structure of a gamelan piece, called the balungan, is grouped into four-beat units...

, following the rules of the pathet

Pathet

The pathet is an organizing concept in gamelan music. It is difficult to explain, but is similar to the melody types, that is, for example, modes, ragas, or maqamat, of other musics....

 of the piece.

The most elaborate cengkok repertoire is that of the gendér barung. The gambang

Gambang

A gambang, properly called a gambang kayu is a xylophone-like instrument used among peoples of Indonesia and the southern Philippines in gamelan and kulintang, with wooden bars as opposed to the metallic ones of the more typical metallophones in a gamelan...

 and siter

Siter

The siter and celempung are plucked string instruments used in Javanese gamelan. They are related to the kacapi used in Sundanese gamelan....

, on the other hand, do not have such formalized sets of cengkok, and therefore may vary more from performer to performer.

Most cengkok derive from the vocal repertoire, and many have names that originally came from lyrics, like the well-known Ayu kuning. They may incorporate pre-existent melodic patterns through a process of centonization

Centonization

In music centonization is a theory about the composition of a melody, melodies, or piece based on pre-existing melodic figures and formulas...

.