“Midriff” derives from “mid-” and a very old word for the belly. Fashions which bare the belly expose the midriff. People think of the gap being created by scanty tops and bottoms as a rift, and mistakenly call it a “midrift” instead. In earlier centuries, before belly-baring was in, the midriff was also the piece of cloth which covered the area.
BUY THE BOOK!