Lean is an operational strategy that focuses on eliminating waste to improve quality, reduce costs and lead times, and increase customer satisfaction. It involves identifying value from the customer's perspective and mapping the workflow to create an uninterrupted flow. Key lean principles include identifying value streams, minimizing waste, and continuously improving through tools like 5S, visual controls, and plan-do-check-act cycles. Lean thinking emphasizes respect for people, continuous improvement, and understanding customer needs.