Definition by Merriam-Webster (selected part):
In a technology context, lean means reducing waste to enable, maximize the utilization of resources and capabilities to create maximum value in a given context.
In manufacturing – non wasteful of resources (1st generation)
In product development – non wasteful of potential (2nd generation)
Lean is a state of mind for a person. An aspiration for an organization. Becoming lean is a never ending journey
Lean is about not wasting opportunity – aka being fit to get the most out of your opportunity