Unfold

Unfold is a term used in several domains. In general usage, to unfold means to open or spread something that is folded, or to reveal something gradually as events unfold.

In mathematics and computer science, unfold denotes a construction that generates a data structure from a seed value, the dual of a fold. In functional programming, unfold (such as unfoldr in Haskell) produces lists or trees by repeatedly applying a function until a termination condition is met.

In geometry and manufacturing, unfolding refers to the process of transforming a three-dimensional object into a two-dimensional net that can be cut and folded back into the original shape; this is central to sheet metal design, woodworking, and origami.

In biology, unfolding describes the loss of native structure in proteins or other macromolecules due to heat, pH, or denaturants; it is accompanied by the unfolded protein response (UPR) in cells to restore proteostasis.

In popular software, Unfold is the name of a mobile application that provides templates for creating visual stories and posts for social media platforms, notably Instagram; it is marketed as a toolkit for designers and content creators.

Other uses include literary or narrative contexts where a plot unfolds over time. See also folding, denaturation.