A keyword is a reserved word that has an inherent meaning to the compiler and thus cannot be used as an identifier within the language. Keywords often represent a language's possible reference values and statements. They are always written in lowercase, so in case-sensitive languages such as C versions of the same word that are not all lowercase can be used as identifiers.
Reference Values: - double - int - char - string - enum - void
Statements: - break - if / else - for / foreach - switch / case / default - do / while - return