A gatra ("embryo" or "semantic unit"[1]) is a unit of melody in Indonesian Javanese gamelan music, analogous to a measure in Western music. It is often considered the smallest unit of a gamelan composition.
A gatra consists of a sequence of four beats (keteg), which are filled with notes (or rests, pin) from the balungan. In general, the second and fourth beats of a gatra are stronger than the first and third, and the final note of a gatra, called the seleh, dominates the gatra. In other words, the gatras are like Western measures in reverse, with the strongest beat at the end. Important colotomic instruments, most notably the gong ageng, are played on that final beat. If the final beat in a gatra is a rest, the seleh is the last note played. It is not uncommon in gamelan repertoire to find entire gatras of rests. Note that the actual length of time it takes to play a gatra varies from less than a second to nearly a minute, depending on the tempo (laya) and the irama.
In kepatihan notation, gatras are generally grouped together in the notation of the balungan, with space added between them. There is, however, no pause between one gatra and the next. The different patterns of notes and rests in a gatra are explained at balungan.
Rahayu Supanggah considers the hierarchical nature of the four beats of a gatra to be reflected on a larger scale in gamelan compositions; in particular by the four nongan in a gongan of the merong and inggah of a gendhing. This is similar to the padang-ulihan ("question-answer") structure key to gamelan composition.[2]