A web application is interactive software built into a website. Web applications often include online databases and allow users to submit or retrieve information interactively.
Web applications present content dynamically, meaning that users are presented with up-to-the-second information each time they view a page.
The shopping carts used on ecommerce sites are examples of web applications. Information is sent back and forth between your computer and the shopping cart application, which keeps track of your items and calculates your total.