Nappe fold structure refers to the large-scale folds associated with the formation of nappes during compressional tectonics. These structures are key features in understanding the deformation processes involved in orogeny and the tectonic evolution of mountain belts.
Reference: Ramsay, J. G., & Huber, M. I. (1987). “The Techniques of Modern Structural Geology, Volume 2: Folds and Fractures.” Academic Press.