Tapioca is a starch extracted from the storage roots of the cassava plant, a species native to the North and Northeast regions of Brazil, but whose use is now spread throughout South America. It is a perennial shrub adapted to the hot conditions of tropical lowlands. Cassava copes better with poor soils than many other food plants.
Tapioca is a staple food for millions of people in tropical countries. It provides only carbohydrate food value, and is low in protein, vitamins and minerals. In other countries, it is used as a thickening agent in various manufactured foods.
Info from Wikipedia