Wow, that Jini entry in wikipedia is really terse. I found this quote attributed to the Jini specification book:
"Jini technology is a simple infrastructure for providing services in a
network, and for creating spontaneous interactions between programs that use these services. Services can join or leave the network in a robust fashion, and clients can rely upon the availability of visible services, or at least upon clear failure conditions. When you interact with a service, you do so through a Java object provided by that service. This object is downloaded into your program so that you can talk to the service even if you have never seen its kind before - the downloaded object knows how to do the talking. That's the whole system in a nutshell."
So the basic idea is a way of creating a loose network of communicating applications that does not break when any component goes offline and hides details of services. Very much in the current mode of web services, SOA and
"Grid" computing. Bill