literally 'small stomach'; commonly used to mean a slight hunger or the lower part of the stomach area (e.g., 'to be a little hungry').
午後三時ころ、小腹がすいてお菓子を食べた。
Around three in the afternoon I felt a little hungry and ate a snack.
長時間の会議の合間に小腹を満たすものを持ってきてください。
Please bring something to stave off slight hunger during the long meeting.
夜遅くに小腹が空くと、軽いものを食べることが多い。
When I get a little hungry late at night, I usually eat something light.