Middleware is one of those tricky words that more or less describes what it does. It is software that connects different parts of an application or a series of applications. It can be though of as a sort of glue that holds a network and its connected computers together. Middleware can be a single application, or it can be an entire server.
People can also think of middleware as an adapter device that would run from a new printer to an older computer. The adapter connects the two devices, enabling communication — and, therefore, functionality — between them. Common packages include the Distributed Computing Environment (DCE) and the Common Object Request Broker Architecture (CORBA).
Every type of middleware has the same general purpose: to allow multiple computers to do multiple things across a network, or to allow one computer to do many things or one complicated thing across a network. For example, some is used to link a database system to a Web server, allowing users to access the database via a Web browser. Certain complicated computer systems require this type of software in order to run their demanding applications. A perfect example of a large form of middleware is an application server, which is a server that is dedicated to a single application or a single type of application.
Another example would be a suite of software that helps serve an online gaming environment. More and more frequently, online games feature high-definition, high-resolution, graphic-intense presentations. Traditional server solutions are no longer enough to facilitate such online gaming experiences, especially if they are multi-player. Middleware helps bridge the gap, both in reality and in virtual reality.
At its most basic, middleware is invisible, allowing computers to connect and communicate with one another and with servers. Without this software, certain kinds of network activity would be impossible. The more powerful applications become, the more middleware will be needed.