An antiform is a fold that has the shape of an arch, but unlike an anticline, it does not necessarily have the oldest rocks at its core. The term is used when the age relationships between the strata are unknown or irrelevant. Antiforms are important in the study of fold structures and tectonic deformation, providing information on the stresses and forces that have shaped a region’s geology.
Source Ramsay, J. G. (1967). Folding and Fracturing of Rocks. McGraw-Hill.