Undo is a command included in most software programs. It is typically located at the top of the Edit menu and has the standard shortcut "Control+Z" in Windows and "Command-Z" in Mac OS X. The Undo command allows you to undo the last action you performed in the program. Many programs also include a "multiple undo" feature, which allows several actions to be undone in series. You can typically reverse an "Undo" command by selecting "Redo" from the Edit menu.
The Undo command can undo a wide variety of actions, depending on the program. For example, in a word processor, Undo is often used to delete a recently typed section of text. However, you can also undo a deletion, the pasting of an object, or a change made to the page formatting settings. In an image editing program, you can undo a paintbrush stroke, a selection, the moving of an object, and many other actions. Modern operating systems allow you to undo moving and renaming files.
Undo is a convenient feature, which can save a lot of time and frustration for those of us who are not perfect and occasionally make mistakes. Perhaps that's why the shortcut was designed to be so easy to use (Z is right next to the Control and Command keys). So, whenever you make a mistake while using a program, just enter the Undo shortcut and the mistake is gone. If only the Undo command could be used in other areas of life as well.