The iterative model is a software development approach where requirements are defined and implemented in increments, with each increment building on the previous ones. In each iteration, a small part of the software is specified, developed, tested, and reviewed to identify additional requirements. This process is repeated until the full product is complete. The iterative model allows requirements to evolve over time through user feedback on early versions. It has advantages like early defect detection and user input, but risks costly late-stage changes from unclear initial requirements. The iterative approach is best for large projects where major requirements are defined but details can change.