Tapioca is derived from roots of Manihot esculenta, a South American plant, which became widely grown in the tropics, esp. SE Asia.
It has several names- cassava, manioc, yuca (not yucca), and others.

No way the Japanese could have destroyed it everywhere; in SE Asia they used large quantities to feed their soldiers, so it was hard for civilians to get until new crops were planted after the War.

Tapioca is gluten-free and almost protein- free.
It is used to make pearl tapioca (various sizes of 'pearls') and, when powdered, used for thickening.

We prefer tapioca starch to corn starch when we thicken soups or sauces; to us, corn starch has a flavor that sometimes clashes with the other ingredients in a sauce so we substitute tapioca starch, which is easy to get in our multicultural city.
Pearl tapioca is a favorite dessert of ours, but the supermarket deli in our neighborhood makes it now, so we buy it there rather than prepare it in the kitchen.

Green-branched manioc has a toxin which must be removed; the natives of Brazil knew how to remove it, and cassava or manioc was an important food to them before the Europeans came.

'Pearl' tapioca can be made from the sap of the sago palm, but is not the same thing, although it can be used in similar ways.
Arrowroot is sometimes confused with pearl tapioca.