siding
noun
°A building material which covers and protects the sides of a house or other building.
"Ugh. If there's one thing I can't stand it's cheesy vinyl siding."
°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).
synonyms: railroad siding, sidetrack, lay-by