Midriff is the standard form of the noun referring to the middle part of the human body, especially the portion between the bust and waist. It comes from Old English, where the prefix mid- meant the same as it does today, and hrif meant belly. Midrift is a misspelling. It is common, but it tends to give way to midriff in edited writing.
Two-piece styles that cover all but a sliver of your lower midriff are another option. [Wall Street Journal]
The corpse of one of Gaddafi’s men was sprawled there, blood covering his midriff and his combat trousers. [Guardian]
The 21-year-old showed his anger at a lingering tackle by Port Adelaide’s Kane Cornes on Saturday night by jabbing the veteran Power midfielder in the midriff. [Sydney Morning Herald]