A programmable logic controller (PLC) is an industrial digital computer designed to control manufacturing processes or machinery. It uses a programmable memory to store instructions for specific tasks, allowing it to automate operations like assembly lines, robotic devices, and other equipment. PLCs are known for their reliability and ability to withstand harsh environments. PLCs operate by receiving input signals from sensors and switches, processing the information based on the programmed logic, and then sending output signals to actuators and motors. This enables real-time control and monitoring of various industrial processes, improving efficiency and safety in operations.