en.wikipedia.org/wiki/Java_Message_Service

Messaging is a form of loosely coupled distributed communication, where in this context the term 'communication' can be understood as an exchange of messages between software components. Message-oriented technologies attempt to relax tightly coupled communication (such as TCP network sockets, CORBA or RMI) by the introduction of an intermediary component. This approach allows software components to communicate 'indirectly' with each other. Benefits of this include message senders not needing to have precise knowledge of their receivers.

The advantages of messaging include the ability to integrate heterogeneous platforms, reduce system bottlenecks, increase scalability, and respond more quickly to change.^[4]

The Java Message Service (JMS) API is a Java Message Oriented Middleware (MOM) API^[1] for sending messages between two or more clients. It is an implementation to handle the Producer-consumer problem. JMS is a part of the Java Platform, Enterprise Edition, and is defined by a specification developed under the Java Community Process as JSR 914.^[2] It is a messaging standard that allows application components based on the Java Enterprise Edition (Java EE) to create, send, receive, and read messages. It allows the communication between different components of a distributed application to be loosely coupled, reliable, and asynchronous.^[3]

http://www.oracle.com/technetwork/java/faq-140431.html#what_is_jms

Q: What is the Java Message Service? 
A: The Java Message Service (JMS) API is an API for accessing enterprise messaging systems. It is part of the Java 2 Platform, Enterprise Edition (J2EE).

The Java Message Service makes it easy to write business applications that asynchronously send and receive critical business data and events.

The Java Message Service defines a common enterprise messaging API that is designed to be easily and efficiently supported by a wide range of enterprise messaging products.

The Java Message Service supports both message queueing and publish-subscribe styles of messaging.