Tapioca is a refined starch obtained from the root of the cassava plant Manihot esculenta, which is also variously known as manioc and yuca. Cassava is native to South America, but is now extensively grown in tropical regions the world over and is among the top half dozen cash crops of the tropics.
Cassava has a very high starch content at 24 %, most of which is stored as food reserved in the root of the plant. Cassava starch has an interesting property of forming into a stringy mass once dissolved in water; so most tapioca is sold as small balls, or pearl tapioca.
Pearl tapioca is manufactured by extracting the juice from cassava roots leaving just the pulp. This pulp is soaked in water, then kneaded to release as much starch as possible. The fibrous remains of the root are strained away and the resultant liquid is dropped onto a hotplate, where they dry, gelatinize and form into the familiar pearls. Tapioca is also sold in flour form, which is simply known as tapioca starch.
Tapioca starch is used as a thickening agent, in much the same manner as cornflour (cornstarch), while tapioca pearls are generally used in sweet dishes. South-East Asia has become the spiritual home of pearl tapioca desserts, where a bewildering array of differently scented confections can be found. Contrary to popular belief, a well-made tapioca pudding is actually quite delicious.