Chillum refers to a specific apparatus design where two opposing notches or dents are made in the body of the pipe to allow the user to place the pipe in between the ring finger and the pinky finger and hold the Chillum in place. The user then cups both hands together to make a relatively airtight chamber, flexes the thumb to create a small hole, presses lips to the thumb hole and inhales. Chillum is used interchangeably with Onie, One Hitter and Cigarette Holder, though functionally, it is not the same by nature of the dents made for the holding fingers.
Most ascribe this apparatus to India as a method of hygenic smoking where the lips of the user never actually touch the pipe. With the advent of glass pipes however, the function of this apparatus is just ceremonial; a glass pipe can be sterilized at the mouthpiece simply by passing an lit lighter over it a few times.