EXIT

Quits the MS-DOS command interpreter (COMMAND.COM) and returns 
to the program that started the command interpreter, if one 
exists.

Note:
"The program that started the command interpreter":
It can be like this: In QuickBASIC, you select: 

FILE -> DOS Shell

Then QuickBASIC will start a new instance of command 
interpreter for you. There, if you type "EXIT", you will return 
to QuickBASIC.

For more information, please refer to MS-DOS Help or Windows NT 
command line command help.