Undo

A function in most computer programs with some type of editing feature that allows the user to reverse, or undo a change that has just been made, thereby reverting the open document to the state it was in prior to the change. Most programs that have an undo capability also have a redo function, which simply reinstitutes the change. Nowadays many programs have expanded on this function and allow many levels of undo so a user can step back through a long history of modifications and revert them back to how they were before the changes.