A normal fault is a type of fault where the hanging wall moves downward relative to the footwall, typically associated with extensional tectonic regimes. Normal faults are significant in understanding the processes of crustal extension, the formation of rift valleys, and the development of sedimentary basins.
Reference: Twiss, R. J., & Moores, E. M. (2007). “Structural Geology.” W. H. Freeman.