Industrial IoT (IIoT) systems connect sensors, machines, and control systems on factory floors, power plants, refineries, and large-scale infrastructure. Data flows from thousands of sensors → local edge gateway → cloud for storage and analytics. The challenge is real-time reliability, low latency, security in air-gapped networks, and handling massive data streams. Unlike consumer IoT, IIoT demands extreme uptime (99.99%+) because manufacturing downtime costs $1M+/hour. Architecture prioritizes resilience over elegance.