Production methodology reliant on heijunka and characterized by single piece flow production accomplished according to takt time and pull production to use the absolute minimum resources to make only what is needed – when it is needed.
JIT is a result of single piece flow, adherence to takt time, and pull rather than a lean concept itself. It is not something you can start tomorrow, yet it is a pillar of the Toyota Production System. Because of the misunderstanding of the complexity of JIT people tend to blame JIT for any shortage experienced early in a lean "journey," even when the three elements necessary for JIT are still being built. For this reason, early in any lean transformation all employees should be made to understand JIT and be assured that processes that have it will be made known.