definition
A second, relatively short length of track just to the side of a railroad track, joined to the main track by switches at one or both ends, used either for unloading freight, or to allow two trains on a same track to meet (opposite directions) or pass (same direction); a railroad siding.
definition
(sometimes) Any auxiliary railroad track, as differentiated from a siding, that runs adjacent to the main track.
definition
A smaller tunnel or well drilled as an auxiliary off a main tunnel or well.
definition
An alternate train of thought, issue, topic, or activity, that is a deviation or distraction from the topic at hand or central activity, and secondary or subordinate in importance or effectiveness.
example
Stay focused on the story; you keep getting lost in all of these little sidetracks.