A website is a group of related and interlinked web pages published by the same owner on the same domain, typically used for information or marketing purposes with limited interactivity. On the other hand, a web app is an interactive piece of software that runs in your browser, offering complex functionality and allowing users to accomplish specific tasks. Key differences between websites and web apps include interactivity, scalability, user profiles and authentication, functionality, underlying technologies, cost, and development requirements. Web applications are generally more complicated and expensive to develop than websites but offer way more possibilities and functionality.