Define the Prototyping Model
In this model, a working model of actual software is developed originally. Prototype is just like a sample software having low reliability and lesser functional capabilities and it doesn't undergo through the rigorous testing phase. Developing a working prototype in first phase overcomes the drawback of the waterfall model where reporting about serious errors is possible only after completion of software development.
Working prototype is given to customer for operation. Customer, afterits use, gives feedback. Analysing the feedback given bythe customer, developer refines, adds requirements and prepares final specification document. Once prototype becomes operational, actual product is developed using normal waterfall model.