A web application is a software product you use through your browser, without needing to install anything. Think of a tool for employees to create quotes, an internal planning system, or a dashboard that combines data from multiple sources. Well-known web applications include marktplaats and bol.com.
A web application stands on its own. The logic, data, and functionality are all contained in a single, self-contained solution and are designed for one purpose, for one target audience. No separate portal for end users, no extensive admin panel for a platform owner. Just a focused tool that solves a specific problem.