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1.
A bicycle, or at least most of the configuration of a standard bicycle, outfitted with additional parts that make it possible to ride the bicycle on a railroad track.
I ride my railbike on the abandoned railroad track that passes by my house.

Railbikers who ride their railbikes on a railroad without permission from the railroad owner are referred to as 'bootleggers'.
by Dick Bentley February 18, 2009