A chillum is a straight conical pipe made of clay or stone, a few inches long. There is generally a small stone inserted in the stem as a stopper containing a hole in the center and/or slits on margins that prevent debris but allow smoke to pass by. 

Such pipes in varied forms were in use by societies across Asia, Africa, and the Americas for smoking herbs. At times, their use was associated with spiritual rituals. In India, chillum use became popular in the eighteenth century. 

Some Indian sadhus used chillums to smoke cannabis, opium, or tobacco with some sort of a spiritual connection with the lord Shiva. Chillums are becoming popular again and are now made with a variety of materials beyond clay (glass, wood, etc.) with various engravings, including cultural symbols.

This sketch is of an Indian Sadhu (ascetic and/or monk) smoking a chillum and is based on a photograph (CC license) by Vijay Richhiya.