Umbul-umbul, also called rérontek or, archaically, tunggul, are a type of flag or pennant made of a strip of cloth whose longer side is attached to a pole. They are used in the traditional culture of Java and Bali, Indonesia, where they are carried in festivals and serve other decorative purposes.
Etymology
A Sundanese language dictionary of 1862 translates the word "umbul-umbul" as "a banner; any signal, as a flag or other object, hoisted so as to be seen at a distance. Banners carried about the person of native chiefs. A small flag attached to a spear." It also notes that the same word, pronounced differently, means "to come in sight, to show up".
References
Umbul-umbul Wikipedia(Text) CC BY-SA