In this article Keywords are predefined, reserved identifiers that have special meanings to the compiler They cannot be used as identifiers in your program unless they include @ as a prefix For example, @if is a valid identifier, but if is not because if is a keyword The first table in this topic lists keywords that are reserved identifiers in any part of a C# program Contents Keywords are the words and phrases that people type into search engines to find what they're looking for For example, if you were looking to buy a new jacket, you might type something like "mens leather jacket" into Google Even though that phrase consists of more than one word, it's still a keyword What is a keyword? A Keyword Primer Finding And Using Keywords Effectively Act On Keyword definition computer