The significance of end-user testing in application design lies in its ability to provide real-world feedback from actual users during the development process. This testing phase reveals usability issues, functionality gaps, and user preferences, allowing designers to make informed adjustments. Engaging end users early in the design process increases the likelihood of creating a product that meets their needs and expectations. By validating design choices based on user feedback, organizations can reduce the risk of costly revisions post-launch and enhance overall user satisfaction with the final product.