HTTP is request-response. The server can't push data to the client without being asked. For real-time features (chat, notifications, live updates), you need different approaches.
Long polling: Client sends request. Server holds it open until data is available or timeout. Client immediately sends another request. Simple but inefficient.
WebSockets: Full-duplex connection. After initial handshake, both sides can send data anytime. Lower latency, more efficient for frequent updates. Use for chat, gaming, live collaboration.