Complex sentence: A web application or web app is any application software that runs in a web browser and is created in a browser-supported programming language (such as the combination of JavaScript, HTML and CSS) and relies on a web browser to render the application.
Split into simpler sentences: A web application or web app is any application software that runs in a web browser. It is created in a browser-supported programming language (such as the combination of JavaScript, HTML and CSS) and relies on a web browser to render the application.