Also an
acronym for
Flashing
Rear
End
Device (or Fucking Rear End Device, depending on who you ask.) Sometimes known affectionately as "Freddy", it's the little blinking
red light on the end of a freight
train. The FRED serves as both a
telemetry device, sending information about the train to the
engineer, and to make the train visible at night.
In a railroad yard, if a train has a FRED attached, it is an active train, and could leave at any minute. This is useful information for train-hoppers and the like.