While textbook Chinese teaches 你好 (Nǐ hǎo) as the universal greeting, in everyday life acquaintances and neighbors frequently greet each other with:
This greeting originated in China's historical agrarian society, where food security was a community's foremost concern. Asking if someone has eaten is not an invitation to lunch; it is an expression of deep, caring empathy—equivalent to "How are you doing today?"
How to respond: Simply smile and say 吃了,你呢? (Chī le, nǐ ne? · I've eaten, and you?) even if you have not eaten yet!