4 Definitions

Any activity that does not contribute to the value of a process as defined by that process’ customer.
Activity which uses resources but which does not add anything which the customer wants to the product or service. Sometimes called Type 2 Muda. Compare Value Added.
Activities which are essential tasks that have to be done under present working conditions but don't add value to the product (sometimes referred to as required waste). The desire is to either minimize these activities or introduce process improvements that would eliminate them entirely.
defined by Beyond Lean
Any activity that does not add form, feature or function to the product. Non Value Added activities include transportation, storage, inventory/buffers, handling, queues, machine repairs, etc
defined by Lean Kaizen