(1) Before the Web, the term referred to a computer in a client/server environment that performed the business logic (the data processing). In a two-tier client/server environment, which is most common, the user's machine performs the business logic as well as the user interface, and the server provides the database processing. In a three-tier environment, a separate computer (application server) performs the business logic, although some part may still be handled by the user's machine. After the Web exploded in the mid-1990s, application servers became Web based (see definition #2 below). See file server.

(2) Since the advent of the Web, the term most often refers to software in an intranet/Internet environment that hosts a variety of language systems used to program database queries and/or general business processing. These scripts and services, such as JavaScript and Java server pages (JSPs), typically access a database to retrieve up-to-date data that is presented to users via their browsers or client applications.

The application server may reside in the same computer as the Web server (HTTP server) or be in a separate computer. In large sites, multiple computers are used for both application servers and Web servers (HTTP servers). Examples of Web application servers include BEA Weblogic Server and IBM's WebSphere Application Server. See Web server.