A visual signaling system for pull-production — physical cards (kanban literally means "signboard" or "visual card") that authorize production or movement of materials. When a downstream process consumes parts, the kanban card returns upstream, authorizing the production of replacement parts. No card, no production. taiichi-ohno was inspired by visiting American supermarkets in the 1950s: items on shelves are replenished only when customers pull them. The supermarket insight was one of TPS's founding moments. Kanban makes just-in-time operationally visible — inventory levels, production status, and bottlenecks are immediately apparent. The concept was later adapted for software development by David Anderson as "Kanban for knowledge work," where task cards on boards visualize workflow and limit work-in-progress (see tps-to-lean-software-transmission). Described in toyota-production-system-beyond-large-scale-production and workplace-management.