Just-in-Time (JIT) is a management philosophy that focuses on minimizing the resources necessary to add value to your products and to operate your factory in ways that eliminate waste. Resources are labor, materials, equipment, space, and time. Waste is anything that does not add value to your products. Moving work-in-process from place to place, stacking and sorting, investing capital in large work-in-process and raw material inventories, inspecting materials at your vendors' sites, and tying up warehouse space with finished goods are all activities that add cost, not value, to your products.
JIT is a process that reduces lead time. JIT does not replace an MRP, an inventory program, a scheduling technique to bypass your Master Schedule, or a materials management project. JIT is the never-ending commitment of everyone, from top management to your workers on the floor, to maximize your effectiveness through continuous, incremental improvements.