To return to a previous state by undoing the effects of one or more commands. The undo command is a valuable feature supported by many software products. It lets you try unknown commands with less risk, because you can always return to the previous state. Also, if you accidentally press the wrong function key, you can undo your mistake.
Many programs allow you to undo an unlimited number of commands. Each time you press the undo key, the previous command is undone. You can roll back an entire editing session this way. Other programs impose a limit on the number of commands you can undo.