Application

Application servers, whatever their function, occupy a large chunk of computing territory between database servers and the end user. Most broadly, this "country" is called "middleware" and that tells you something about what application servers do. First and foremost, application servers connect database information (usually coming from a database server) and the end-user or client program (often running in a Web browser). There are many reasons for having an intermediate player in this connection -- among other things, a desire to decrease the size and complexity of client programs, the need to cache and control the data flow for better performance, and a requirement to provide security for both data and user traffic.