`打招呼` is more than just a polite gesture in Chinese culture; it's a fundamental part of maintaining social harmony (和谐, héxié) and showing respect. The act of acknowledging others, regardless of how brief, reinforces social bonds and reaffirms everyone's place within the community or group. A key cultural difference lies in the *purpose* of the greeting. In many Western cultures, a greeting like “How are you?” can be an invitation to a short conversation. In China, the act of `打招呼` is often sufficient in itself. For example, the famous greeting “你吃了吗？(nǐ chī le ma?)“—”Have you eaten?”—isn't usually a genuine inquiry about your dietary habits. It's a functional, classic way to `打招呼`, to show you care and to acknowledge the other person. The expected answer is usually a simple “吃了 (chī le),” even if you haven't. Ignoring someone and failing to `打招呼`, especially an elder, a superior, or someone you know, is considered very rude. It can cause the other person to “lose face” (丢面子, diū miànzi) and can damage your `关系 (guānxi)` or relationship. The simple act of a nod or a “嗨 (hāi)” goes a long way.
`打招呼` is used constantly in daily life, but its meaning can shift based on context.
This is the most common usage. It describes the action of acknowledging someone you see.
This is a crucial, more nuanced meaning that often confuses learners. It means to let someone know about something in advance, often as a courtesy or to get implicit approval.
The key difference is that the “greeting” meaning happens when you see someone, while the “heads-up” meaning happens *before* an event.