A programmable logic controller (PLC) is a digital computer used for automation of industrial processes. It monitors inputs from various sensors and devices, processes the information, and controls outputs to machinery or systems based on pre-defined logic. PLCs are designed to be robust and reliable, making them suitable for harsh environments. PLCs can be programmed using various languages, including ladder logic and structured text, allowing engineers to customize their operation. They are widely used in manufacturing, assembly lines, and other automated systems to improve efficiency and reduce human intervention in repetitive tasks.