"e-business" middleware from IBM, based around Java technology. Some of the technologies involved include servlets, JavaServer pages, XML, Java Beans, EJB and CORBA.
Essentially a suite of technologies for companies wishing to integrate their business with the web, it is designed around the WebSphere Application Server and WebSphere MQ.
WebSphere Studio is the most important component for developers, along with much other supporting software such as VisualAge for Java.
It is a large suite, and there are many other products available as part of or for use with it, such as WebSphere Commerce Suite (for e-commerce support) and Lotus Domino.