Service container docs, reference section

glossary.rst

@@ -23,4 +23,22 @@ Glossary
         A *Front Controller* is a short PHP that lives in the web directory
         of your project. Typically, *all* requests are handled by executing
         the same front controller, whose job is to bootstrap the Symfony
-        application.
+        application.
+
+    Service
+        A *Service* is a generic term for any PHP object that performs a
+        specific task. A service is usually used "globally", such as a database
+        connection object or an object that delivers email messages. In Symfony2,
+        services are often configured and retrieved from the service container.
+        An application that has many decoupled services is said to follow
+        a `service-oriented architecture`_
+
+    Service Container
+        A *Service Container*, also known as a *Dependency Injection Container*,
+        is a special object that manages the instantiation of services inside
+        an application. Instead of creating services directly, the developer
+        *trains* the service container (via configuration) on how to create
+        the services. The service container takes care of lazily instantiating
+        and injecting dependent services.
+
+.. _`service-oriented architecture`: http://wikipedia.org/wiki/Service-oriented_architecture