Lean
Lean is a management philosophy, originating at Toyota, focused on eliminating waste – anything that costs time or resources without adding value for the customer.
Toyota developed it after WWII as a small manufacturer competing against much larger rivals, refining a system around seven wastes: overproduction, waiting, transport, over-processing, inventory, motion, and defects. The core principles – pulling work from customer demand rather than pushing it from production, and treating perfect quality as the target rather than an acceptable defect rate – are what took Toyota from a small manufacturer to a world leader in quality.
Lean is an improvement instrument for the process you already have, not a redesign method – which is what separates it from something like business process reengineering.
See Lean process improvement in practice – removing the waste, step by step.