A manufacturing unit uses colour-coded cards to signal when materials must be replenished from the previous process stage. Production starts only when such a signal is received. This system ensures demand-driven production. Which Lean tool is being applied?

Kanban is a Japanese term meaning "signboard" or "signal card". It is a visual management tool used in a Pull System to trigger the production or replenishment of items only when they are consumed. In this system: 

• Visual Signals: Colour-coded cards or bins are used as signals to indicate that materials have been used.
• Demand-Driven: Work starts only when a signal is received from the subsequent stage (the "customer"), ensuring production is driven by actual demand rather than forecasts.
• Waste Reduction: By limiting work-in-progress (WIP), it prevents overproduction and reduces inventory costs. 

  Note: Poka-Yoke is a Japanese term that means "mistake-proofing". A poka-yoke is any mechanism in a lean manufacturing process that helps an equipment operator avoid (yokeru) mistakes (poka). Its purpose is to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur. The concept was formalised, and the term adopted, by Shigeo Shingo as part of the Toyota Production System. It was originally described as baka-yoke, but as this means "fool-proofing" (or "idiot-proofing") the name was changed to poka-yoke.