People referring to National Rail services as traveling 'Overground'
If you've lived all your life in London, especially if you're north of the river, where most local trains are "the underground", then if you need to do a local London journey to somewhere which only has "main line" trains (eg most places south of the river), then it was always normal parlance to say something like "I'm going to X, so I'll have to get the overground". All my family, and pretty much all long-time Londoners I know, have referred to "proper" (main line) trains as "the overground", to distinguish them from underground system. It was - and for many still is - the normal terminology, and perfectly natural and understandable. I presume it started - maybe even as a joke somewhere - soon after "the underground" (or should I say "the Underground"?) got started generations back.
It's TfL who've caused confusion and ambiguity by branding the subset of "proper" London train lines they control as "the Overground" with a capital O. (Clearly that decision wasn't taken by actual Londoners!) So now there's the situation of some Londoners of my acquaintance, when referring to getting "the overground", stopping to qualify whether they mean "with a small o" or "with a big O". Indeed, for those not really "following" transport issues, and getting a local train in London only very occasionally, I'd say that most wouldn't know which was officially the Overground and which just the generic "overground". It wouldn't seem important to them.
In this connection (of TfL's branding mania), there's the plan to call Crossrail - if/when it ever happens! - the Elizabeth Line, as though it were part of the Underground system. This, combined with putting the Crossrail route on the tube map but not the Thameslink route, seems destined to cause more confusion and inconvenience for people trying to use the services who're not familiar with all the ins and outs of it,
On a separate subject - I was brought up to call the main station in Edinburgh "Edinburgh Waverley", or even just Waverley. And my Edinburgh friends call it that. But if you try to put "Waverley" in a search on the NRE site - or if you're masochistic enough to try to use their phone line, and ask their phone operators - you'll discover that there
is no Waverley, The name isn't recognised as a station name, or even as part of a station name. So are Network Rail right? Have millions of people got it wrong all these years?!