Answer;
Husk.
Whole-grain flour contains all parts of the grain with the exception of the husk.
Explanation;
Whole grain foods contains the following parts; Bran, Endosperm and Germ, originally present before processing.
Refined grains on the other hand are mainly composed of only endosperm portion of the grain. Milling process removes bran and some also removes germ, along with the majority of fiber, vitamins, minerals, antioxidants and phytochemicals.