The Service Assemblies node is a folder containing all service assemblies that are currently deployed to this server.
A service assembly is a single standard document describing the routing, artifacts, and services that make up an SOA application. You can think of a service assembly as an SOA "super .jar file" that packages together the individual service units, modules, and configurations into a single deployable entity.
The pop-up menu of each Service Assemblies subnode allows you to start, stop, shut down, or undeploy it.