Summary: FRED or Flashing Rear End Device is a device mounted at the rear of the train, in lieu of a caboose. The dumb FRED is equipped with a battery powered strobe.
Advanced smart FREDs transmit speed and air line pressure via radio to a receiver in the cab. The receiver, SBU (Sense and Brake Unit, Canada) or HOT (Head-of-train, US) is often referred to as WILMA by railroaders.
FREDs can be modelled using SMT LEDs.
Also see FX_Lighting
Want to build your own FRED? See Flashing Rear-End Device For DCC Systems for a schematic, and many other DCC projects.
Other Uses of the Term
Fireman Fred is a series of sound effects available on Tsunami Decoders by Soundtraxx. Sounds such as shovelling coal, injectors, or water being dumped into the tender are available either by a function key or automatically depending on the situation and programming.