It depends on the user of the terms.
Definition of Work-in-Process
I use the term "work-in-process" to mean a manufacturer's inventory that is not yet completed . I think of work-in-process as the goods that are on the factory floor of a manufacturer. The amount of Work-in-Process Inventory would be reported along with Raw Materials Inventory and Finished Goods Inventory on the manufacturer's balance sheet as a current asset .
Definition of Work-in-Progress
I use the term "work-in-progress" to mean construction of long term assets (that will be used in the company's business) that are not yet completed . For example, if a company is constructing an addition to its building and the work is only partially completed, the amount spent so far would be recorded as Work-in-Progress, Construction in Progress, or Construction Work-in-Progress (CWIP) and the account would be on the balance sheet as a long-term asset in the section entitled Property, Plant and Equipment. When the project is completed and put into service, the amount would be transferred out of CWIP and would be reported in the account Buildings within Property, Plant and Equipment. At that point, the depreciation of the addition will begin. (If a company is constructing an assembly line or a huge machine that will take time to build, the amounts would also be accumulated in CWIP. When the project is completed and is placed into service, the amount will be transferred from CWIP to Equipment and depreciation will begin.)
To complicate matters, companies that produce items under a long-term contract will use an account entitled Construction-in-Process.
Your question points out the need for caution and an understanding of what the communicator intends. Keep in mind that the sender of a message might not realize that there are important differences between slightly different terms.