Nomikomi (飲み込み) – n – literally means “to swallow” in Japanese. In the context of carpentry, nomikomi typically refers to material geometry that allows the edge of one material to be hidden behind that of another, thus eliminating the need for precision-cutting (see tsukitsuke).
The above image shows mikiri-zai acting as a joint between flooring and a wall. This particular mikiri allows the flooring to extend underneath it, concealing the cut edge. Without nomikomi, the flooring would have to be cut to meet the mikiri (tsukitsuke, see link above), which is extremely time-consuming.