A process or result of a gradual change from the original appearance of a material, such as paper, due to aging or environmental changes, or both.
While yellowing in paper is especially pronounced in papers produced from mechanical wood pulps, it occurs to a greater or lesser degree in virtually all types of vegetable fibers.
Usually refers to the yellow fore-edges and pages of paperbacks, which is caused either by fading, age and/or acid in the paper.