The inventory between the start and end points of a production process. (Lean Construction Institute Glossary)
Work-in-Process (WIP) see also Work in Process (WIP) Work-in-process, or WIP, refers to inputs that are still in the operation. Laundry still in the washer, the dryer or being folded would count as WIP in our example (as would laundry in transit to either the washer or the dryer)….
Work-in-Process (WIP) Number of units in the process at any point in time. If the process includes buffer inventories between steps, they the work-in-process is the total number of units being worked upon as well as waiting in the inventory between steps. The units in inventory are usually referred to as Work-in-process inventory, to distinguish them from raw materials inventory or finished goods inventory.(http://hbswk.hbs.edu/pubcontent/toolkit/operations/glossary.html)