WMS (warehouse management system)
A WMS knows where every unit sits in the warehouse and walks people through receiving, picking and shipping. Every movement is confirmed by a scan, so the stock in the system matches the stock on the shelf.
In practice a WMS starts at the dock: the worker scans a pallet or carton, the system compares the delivery against the advice note and assigns the location the goods should go to. From then on every move, pick and shipment goes through a scanner, so nobody has to remember that a batch was shifted from rack A to rack C two weeks ago.
For picking, the WMS groups orders into waves and leads the picker along a path instead of sending them back and forth across the warehouse. The scanner confirms each unit, and a mistake blocks the next line, so a wrong shipment stops inside the warehouse rather than at the customer.
A WMS usually does not replace the ERP. Orders and invoices stay in the ERP, while the WMS owns what happens between goods-in and goods-out and sends confirmed stock and documents back. In Polish companies it is most often connected to Comarch ERP, enova365, SAP Business One or Subiekt, plus carriers and sales platforms.
The signal that you need a WMS is not the size of the warehouse but the gap between the system and the shelf: quarterly stocktakes with discrepancies, picking that depends on one person's memory, and weeks before a new hire can work on their own.