Work in process refers to the partially completed goods in your business. It can cover anything and everything from raw materials to overhead costs and anything else that is used/required to form whatever end product you are going for (at a specific stage within the cycle of production).
Typically, a piece of inventory becomes labeled as work-in-progress when raw material combines with labor. When the product is finalized, it switches from WIP to being categorized as a finished product.
The following functionality around WIP items is covered in DATASCOPE WMS: