The time between operations that change the form or function of a part, typically spent in motion or waiting in a batch until the other pieces in the batch are processed, though the examples can be endless.
Nonvalue-added time can include pure waste, such as that caused by motion or batching. This is defined as Type 1 Muda. Nonvalue-added time can also be ancillary time that is necessary to support the process – it has to be done – but it does not change the form or function of at part. This is defined as Type 2 Muda or incidental or ancillary time. Examples of ancillary time include inspection, reporting, etc. that can perhaps be reduced but not eliminated.
Discussions of whether paint drying or parts cooling is or is not value-added time are pointless. Their duration should be reduced where possible, of course, and treated consistently so that comparisons of production efficiency are not unduly affected.
Lean seeks to reduce lead times by reducing nonvalue-added time within a process.