A massif is a large, stable block of the Earth’s crust that is bounded by faults or flexures. Massifs are resistant to deformation and often form the core of mountain ranges. Studying massifs is important for understanding tectonic stability, the formation of mountain ranges, and the geological history of a region.
Reference: Twiss, R. J., & Moores, E. M. (2007). “Structural Geology.” W. H. Freeman.