Cassava, also known as yuca, is a root vegetable that is dried and ground into a flour.

While tapioca is also derived from the yucca root, cassava flour differs in that it is the whole root - peeled, dried and ground, while tapioca is just the extracted starch.  

Cassava makes a great substitute for wheat flour and is free of allergens. Because it is high glycemic, be sure to consume in moderation.