Well, I think we can put this in order like so:
The term “Staging Yard” has different meanings in the prototype US, Canada, UK, and model RR worlds. In model railroading terms, it is generally intended to represent an “off-layout” location(s), in other words, “the rest of the world”. On prototype RR’s, it takes on a different context, often referring to a track or yard where trains are parked or stored until either they are needed again (think along the wandering warehouses), or until they can be dealt with (such as interchange tracks, or arrival/departure tracks.) On our models, generally speaking, we use staging tracks/yards as a place to deliver our trains, such as, in a previous example, we may model midway from Chicago/St. Louis, and would use “staging yards” to represent either (or both) major cities.
Brad