A PLC (Programmable Logic Controller) is an industrial computer controlling machinery and processes. It has inputs (sensors, buttons) and outputs (motors, lights, solenoids). You write logic—"if input A and input B, turn on output C"—and the PLC runs it thousands of times per second, responding to factory floor conditions. Example: A beverage bottling line has 50 PLCs. Each controls one section: caps at position X, dispenser fills bottle, capping arm tightens. Each PLC reads sensors (bottle present? full?), executes logic, and commands motors (advance conveyor, activate dispenser). If sensor fails, logic stops that section safely, alerts operator.