A web application (or web app) is application software that runs on a web server, unlike computer-based software programs that are run locally on the operating system (OS) of the device. Web applications are accessed by the user through a web browser with an active network connection. These applications are programmed using a client–server model—the user ("client") is provided services through an off-site server that is hosted by a third-party. Examples of commonly-used web applications include: web-mail, online retail sales, online banking, and online auctions.

A web server is computer software and underlying hardware that accepts requests and send responses via HTTP or its secure variant HTTPS, the network protocols created to distribute web contents (web pages, etc.) to client user agents.