Reserved word

1. Often found in programming languages and macros, Reserved words are terms or phrases appropriated for special use that may not be utilized in the creation of variable names.

2. Reserved words are also used in operating systems as a method of identifying a device file or other service. Below is a listing of Microsoft reserved words in MS-DOS and Windows operating systems. When attempting to use any of the below reserved words as a name of a file, or in a command you may encounter and unusual response. For example, attempting to save a file as CON or CON.txt may generate a reserved file name or access denied error or say the file already exists.

Reserved Word What it is
AUX Auxiliary port aka Serial Port COM1
CON Short for console, which Microsoft describes as the display monitor.
COM1 COM port.
COM2 COM port.
COM3 COM port.
COM4 COM port.
LPT1 LPT port.
LPT2 LPT port.
LPT3 LPT port.
NUL NULL
PRN Printer aka LPT1

Also see: Device file, Java reserved words, Operating system terms, Programming terms, Reserved character, Word