Khong bah png is a phrase in the Hokkien dialect, which means "empty stomach" in English. When your stomach is empty, it means that you haven't eaten anything for a while.
Imagine your stomach is like a balloon. When you eat food, this balloon gets filled up and becomes bigger. But when you don't eat anything, this balloon becomes flatter and emptier, like a deflated balloon.
Having a khong bah png feeling can make you feel very hungry and weak, like your body doesn't have enough energy. So it's important to eat healthy food to keep your stomach full and your body strong.