An asymmetrical fold is a geological fold in which the limbs of the fold are not mirror images of each other. One limb is steeper than the other, and the fold axis may be inclined rather than horizontal. Asymmetrical folds are important indicators of the direction and magnitude of the forces that caused the folding, providing insights into tectonic stress and deformation history.
Reference: Davis, G. H., & Reynolds, S. J. (1996). Structural Geology of Rocks and Regions. John Wiley & Sons.