Reserved word

1. A word within a program or programming language that is reserved for special use that cannot be used. Reserved words are often found in programming languages and macros.
2. Reserved words are also used in operating systems as a method of identifying a device or other service. For example, below is a listing of Microsoft reserved words for their MS-DOS and Microsoft Windows operating systems. When attempting to use any of the below reserved words as a name of a file, and/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 error, may say the file already exists, or may cause an access denied error. Because these are reserved words you cannot create a file using any of the below examples.

Also see: Operating system definitions, Programming definitions, Reserved character, Word