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If I've understood correctly, it's where staff will travel on trains as a passenger as part of their duty in order to position themselves for their next working, or to return to their home depot if finishing elsewhere.
It's just referred to as "passing" at my TOC.
I'm pretty sure there's still a Stagecoach South ALX 400 at Aldershot depot(?) running about with flip-dot blinds.
Used to appear on the route 20 (formerly KITE) between Guildford and Aldershot quite a bit.