I heard the term Jet Train from a B&O guy about 15 years ago.
They mean short fast high priority Trailer on Flatcar trains of 10-15 cars.
Jet trains can go cross country or they can act as feeder trains into hubs were the cars are exchaged with a big transcon train of 100 cars. Jet trains were also used a lot when they were mini ramps in smaller citys and markets. (When ramps were just that …ramps).
Today Jet trains are high priority intermodal I guess which means when the clock strikes 5 and you have your trailer at the gate your not getting on that train.
“Jet” was a marketing name for all of the B&O’s Expedited services. The trains were not short by design. More specifically the trains were called “Trailer Jets” or if mixed “Jets”. For example the New York to Chicago Train was called the “Chicago Trailer Jet”. The actual train symbol was either two letters and two or three numbers or four letters. In the case of the Chicago Trailer Jet the train symbol was CHTJ. The eastbound counter part also handled perishables and other hot carload traffic so it omitted the word “Trailer” from its name, it was called the “Philadelphia-New York Jet” symbol PNJT.
Other “Jets” were the “Western Jet”, “Baltimore Jet”, “St.Louis Trailer Jet”, and “Manhattan Trailer Jet”.