A one-hitter is a small pipe meant for just one hit at a time, as the name suggests.One-hitters typically do not have a carb and typically have the bowl facing outward rather than toward the mouthpiece.
Chillums, a straight, conical type of one-hitter that was first used by holy men in India for centuries before spreading to the rest of the world, are the most common name for one-hitters.
The smoker inhales through the top of their hand while holding a chillum between the ring and middle finger in a fist. A carb can be made by opening and closing the hand. Multiple people can use the same device without touching their lips, making it more sanitary (as long as their hands are clean) than other forms of smoking.