A hookah, or kalian, is a traditional Arabic device for smoking tobacco, or indeed any other smokeable substance, operating on the principle of a Water pipe.
Water, or diluted wine, is used to refine and cool down smoke. Substances used for smoking must not be completely dry - an example of commonly used substance is a mixture of tobacco with semi-dried fruit. Instead of being ignited, the substance is heated to a very high temperature - traditionally with the help of an ember. When the user inhales, the substance fumes, but doesn't burn. This helps preserve the substance and refines the smoke.
Hookah are traditionally decorated, and have a very distinctive appearance.