Reserved words are part of the Pascal language, and as such, cannot be redefined by the programmer. Throughout the syntax diagrams they will be denoted using a bold typeface. Pascal is not case sensitive so the compiler will accept any combination of upper or lower case letters for reserved words.
We make a distinction between Turbo Pascal and Delphi reserved words. In TP mode, only the Turbo Pascal reserved words are recognised, but the Delphi ones can be redefined. By default, Free Pascal recognises the Delphi reserved words.