Web application development involves designing, building, testing, and deploying web-based applications to establish an online presence. This process includes creating a user-friendly and visually appealing design, writing the front-end and back-end code, rigorously testing the application to ensure reliability and security, and finally deploying it to a web server. Custom web application development is chosen by businesses to meet specific needs and provide functionalities such as user authentication, database interactions, and real-time updates, making them dynamic and interactive tools for engaging users.