Middleware in computing terms is used to describe a software agent acting as an intermediary, or as a member of a group of intermediaries, between different components in a transactional process. The classic example of this is the separation which is attained between the client user and the database in a client/server situation. The reason for introducing middleware in such a situation is to better service client requests by reducing the number of resource-expensive connections to the database and more efficiently passing the requested data back.
Examples of proprietary middleware software include: Tuxedo, Tibco, Mercator, Vitria. The ObjectWeb consortium is the first world-wide consortium focused on open-source middleware.
Often used as a buzzword.