Lassi is a traditional North Indian beverage, originally from Punjab made by blending yogurt with water, salt, and spices until frothy. Yogurt is mentioned in ancient Indian texts, and so is buttermilk. Yogurt sweetened with honey is used in Hindu rituals. Traditional lassi is sometimes flavored with ground roasted cumin. The Lassi of the Punjab sometimes uses a little milk and is topped with a thin layer of malai, a clotted cream, also known as Devonshire cream. Lassis are enjoyed chilled as a hot-weather refreshment. With a little turmeric powder mixed in, it is also used as a folk remedy for gastroenteritis.
Sweet lassi is a more recent invention, flavored with sugar, rosewater and/or lemon, mango, strawberry or other fruit juice. Saffron lassis, which are particularly rich, are a specialty of Sindh and Jodhpur, Rajasthan in India. Makhaniya lassi is simply a lassi with lumps of butter in it (makhan is the Hindi and Urdu word for butter).
Bhang Lassi is a special lassi that contains bhang, a liquid derivative of cannabis, which has effects similar to other eaten forms of marijuana. It is legal in many parts of India and mainly used for religious purposes, particularly during Holi, when pakoras containing bhang are also sometimes eaten. Rajasthan is known to have licensed bhang shops, and in many places you can buy bhang products and drink bhang lassis. Many guidebooks warn foreign tourists against trying Bhang Lassi because of the risks of serious intoxication.