These events are to do with the control/feedback of a zone group.
General
A zone group is responsible for control of anything that is used by multiple zones.
http://id.webbrick.co.uk/zones/zonegroup
This is the event type for all events to do with the zone group.
zonegroup/n/run
This event source indicates a requirement to run any devices required by the zone group n.
zonegroup/n/stop
This event source indicates there is now no requirement to run any devices required by the zone group n.
zonegroup/n/running
This event source indicates that the zone group n is running.
zonegroup/n/stopped
This event source indicates the zone group n has stopped.