The core difference between a website and a web app comes from the way users interact with them. A website is all about passive output. You may visit a website to check the weather or a sporting result, read a review of a product. Either way, the result is the same. You'll absorb what the website has to offer. A web app is a little different. In addition to passively absorbing data from a web app, you'll also directly interact with – and potentially edit – the contents. As much as a website is defined by output, a web app is primarily concerned with input.