In graphics software, a layer is the term used to describe the different levels at which you can place an object or image file. In the program you can stack, merge or define layers when creating a digital image. Layers can be partially obscured allowing portions of images within a layer to be hidden or shown in a translucent manner within another image, or you can use layers to combine two or more images into a single digital image. For the purpose of editing, working with layers allows you to go back and make changes within a layer as you work.
See also “Graphics Software Terminology” in the Quick Reference section of Webopedia.