PLIs

Plis is the plural form of the French noun pli, meaning a fold or crease. In English-language contexts, plis is used primarily as a borrowed term in two domains: textiles and geology. The word conveys the idea of a folded or pleated structure, whether in fabric or rock.

In textiles and fashion, plis refers to fabric folds created by sewing, gathering, or pressing. Pleats control drape, volume, and the silhouette of garments. Common types include knife pleats, where a sharp, narrow fold runs in a single direction; box pleats, which form a flat, rectangular fold that faces outward; and inverted or accordion pleats, which reverse or alternate directions. Pleats can be stitched, pressed, or left to form naturally with the fabric’s grain, and they may run lengthwise or across the fabric.

In geology, plis appears in some French-language texts to denote folds in rock layers. In English, the standard term is folds, describing the bending of strata along an axis that creates hinge lines and limbs. Fold shapes are categorized by geometry such as anticlines, synclines, and monoclines, and by tightness ranging from open to tight to isoclinal. Key modeling concepts include the axial plane and the fold axis, which help describe the orientation and intensity of deformation.

Etymology and usage notes: plis derives from the French pli, meaning fold. In most English sources, folds or pleats are used as the corresponding terms, with plis appearing mainly as a technical loanword in specialized discussions. See also pleat and pleating.