Lean means "not wasteful" or "economical," not wasting time and energy doing things that don't bring results.

Only doing something that a customer would want you to do or be prepared to pay for and that which is legally required.

Continuous means "on-going," so the meaning would be to stay focused on improvement, not waste time and never give up! Wow!

'Lean' in this sentence is not just ais an adjective. It's a name of a whole system (or phylosopy) in management. I had a Lean technologies training, for instance.