What is the key ingredient in the refreshing North Indian yogurt-based drink known as "lassi"?

Lassi, a popular yogurt-based beverage hailing from North India, owes its refreshing taste and creamy texture to its primary ingredient: yogurt. Typically made from fresh, thick yogurt, lassi can be enjoyed in various forms, including sweet or savory. For sweet lassi, yogurt is blended with sugar and sometimes flavored with fruits like mango or rosewater, resulting in a deliciously indulgent drink perfect for quenching thirst on hot summer days. On the other hand, savory lassi incorporates spices like roasted cumin and salt, offering a tangy and rejuvenating experience that pairs well with spicy meals.