An application in which all or some parts of the software are downloaded from the Web each time it is run. It may refer to browser-based applications that run within the user's Web browser or to rich client applications that resemble local applications.

Browser Based
In a browser-based Web application, the program instructions are contained within the Web page that is retrieved from a Web site. For example, a combination of HTML and JavaScript is commonly embedded in a Web page and executed by the browser. Alternatively, the Web page may cause the browser to launch a Java applet. Java is a full-blown programming language that is more comprehensive than JavaScript. The data for the application may be stored on the Web, locally or in both locations.

Client Based
Web applications may also run without the browser. A client component that is either downloaded each session or that remains in the user's computer interacts with a server on the Web in some manner using standard Web protocols. This is similar to the "client/server" architecture that prevailed in companies before the Internet exploded, except that the server is on the Internet, not the local network. Like browser-based applications, the data may be stored remotely or locally. See rich client, cloud computing, ASP and SaaS.