Web design is the process of planning, conceptualizing, and arranging content online. Web design also includes web apps, mobile apps, and user interface design. Web designers take what's conceptual and translate it into visuals.
Web development is the process of building, creating, and maintaining of websites. It includes aspects such as web design, web publishing, web programming, and database management. It is the creation of an application that works over the internet.
Testing the application after everything seems good-to-go is the most important aspect of the web/app development model. That’s because there are hundreds of things that can go wrong even after you think every inch of the application has been executed correctly.