whoop n. (also whoop-de-do) a bump or undulation in a trail used for riding or racing motorcyles, bicycles, or motorbikes. (source: Double-Tongued Dictionary)
Further reading
Linda from Chapel Hill, North Carolina, gives directions to her remote home by telling people to turn left after the whoopsy-daisy, her term for a sudden dip in the road. There are quite a few colloquial expressions for such abrupt depression or...
The Rockefeller State Park Preserve near Pleasantville, New York, features a fine example of a glacial erratic, a giant rock left behind thousands of years ago by a glacier as it moved. In this case, the word erratic functions as a noun. Both the...