Your definition of a Parliamentary service is incorrect - it is usually a service (can be just once a week) that is run to keep a line open, rather than have to issue a closure notice (required if no service perovided).
Chiltern's Ruislip-West Ealing (was Paddington) is keeping the piece of line through Greenford open from South Ruislip, for example. This runs Mon-Fri only.
And I would add:
..., provide the mimimum service required by the government on letting of the franchise, or maintained only to serve train crew competence across a particular route.
Ghost trains are those which are parliamentary but also those that are not widely advertised. Such as Wandsworth Road - Battersea Park on the Overground.
Ghost stations are either stations only served by parliamentary trains stations (such as Denton) or are only served by a few trains of those scheduled to pass it. Examples include Ardwick, IBM, Chapelton, Portmouth Arms and Pilning.