A child being immunized against polio. Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen). When this system is exposed to molecules that are foreign to the body, called non-self, it will orchestrate an immune response, and it will also develop the ability to quickly respond to a subsequent encounter because of immunological memory.
Windows Audio Device Graph Isolation is an audio file for recent versions of Windows that prevents other applications from modifying audio-related content and plug-ins. The application also serves as the audio engine for Windows.
This is the Audio Device Graph Isolation service, a part of Vista and 7's audio services. The real audiodg.exe is harmless, but like any file it could be infected. If it's not doing anything, it should be fine. The worst that can happen by ending it is your audio goes out, restarting your computer would fix that.