History palette
From The Glossary of Digital Photography
A palette or panel in Photoshop that displays each step, or function, a user has performed on an image. The number of history steps shown is user-selectable in the preferences menu. By having each step displayed, it is easy to step backward (multiple undos) to earlier versions of an image. This information is kept only while the image is open; once the image is closed, the history of how that image was produced is
lost.
