In a non-Web environment, an application server performs the business logic (the data processing), although some business logic may be handled by the user's machine. See file server
An application server in a three-tier client/server environment provides middle tier processing between the user's machine and the database management system (DBMS).
In a private or public Web environment (intranet or Internet), an application server hosts a variety of language systems used to query databases. These scripts and services, such as Active Server Pages (ASPs), Java server pages (JSPs) and Java servlets, typically access a database to retrieve up-to-date data 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 application servers and multiple Web servers (HTTP servers) are used. Examples of Web application servers include BEA Weblogic Server and IBM's WebSphere Application Server. See Web server
Application Servers & Web Servers
There is overlap between an application server and a Web server, as both can perform similar tasks. The Web server (HTTP server) can invoke a variety of scripts and services to query databases and perform business processing, and application servers often come with their own HTTP server which delivers Web pages to the browser.
Java EE Application Server
Application servers have become the middleware for the enterprise as they provide more hooks into many legacy applications. This is a Java EE-compliant application server running only Java and using Enterprise JavaBeans (EJBs) for the business logic. See EJB