fast line
n.— «Fast line—Quickest route around the oval and could be on the outside or inside of the track depending on conditions. This also is called the “groove” or “sweet spot.”» —“Learning the Lernerville lingo” by Paul Kogut Valley News Dispatch (Tarentum, Pa.) May 14, 2004. (source: Double-Tongued Dictionary)
Further reading
What if, instead of being an inanimate object, a dictionary were alive? That’s the idea behind a lavishly illustrated new children’s book called The Dictionary Story (Bookshop|Amazon) by Oliver Jeffers and Sam Winston. This is part of a...