It's tea (usually) that sometimes has milk (if you want milk or non dairy based creamer) that's got some kind of pearl in it, like tapioca pearls. They're very customization from type of tea, if you even do tea, to flavor of tea or milk or no milk, sugar or no sugar, hot or cold or frozen. And the tapioca pearls don't always have to be tapioca pearls, either. I think the name comes from the milk foam/bubbles on the top when you get it with milk.