What is "perboewatan"

Perboewatan (also spelled Perbuatan; apparently a Malay word of uncertain derivation) was one of the three main volcanic cones (the others being Danan and Rakata) on the island of Krakatoa (or Krakatau), in the Sunda Strait, in Indonesia. It was the lowest (400 ft) and northernmost of the cones. Perboewatan was completely destroyed during the 1883 eruption; the site in which the caldera had been is approximately deep.