Sky burial, or ritual dissection, is a funerary practice in Tibet, wherein a human corpse was incised in certain locations and placed on a mountaintop, exposing it to the elements and animals. The locations of preparation and sky burial are understood in the Vajrayana traditions as charnel grounds.

The majority of Tibetans adhere to Buddhism, which teaches rebirth. There is no need to preserve the body, as it is now an empty vessel. Birds may eat it, or nature may let it decompose. So the function of the sky burial is simply to dispose the remains. In much of Tibet, the ground is too hard and rocky to dig a grave, and, due to the scarcity of fuel and timber, sky burials are often more practical than cremation.

(Source: Wikipedia)