The sets of reserved words and keywords in a language often coincide or are almost equal, and the distinction is subtle, so the terms are often used interchangeably. 9 Reserved words and language independence.This makes parsing more difficult with look-ahead parsers necessary. In yet other languages, such as the older languages ALGOL, FORTRAN and PL/I, there are keywords but no reserved words, with keywords being distinguished from identifiers by other means. In some languages, like C or Python, reserved words and keywords coincide, while in other languages, like Java, all keywords are reserved words, but some reserved words are not keywords – these are "reserved for future use". In general reserved words and keywords need not coincide, but in most modern languages keywords are a subset of reserved words, as this makes parsing easier, since keywords cannot be confused with identifiers. The terms "reserved word" and "keyword" are often used interchangeably – one may say that a reserved word is "reserved for use as a keyword" – and formal use varies from language to language for this article we distinguish as above. By contrast, names in a standard library but not built into the language are not considered reserved words or keywords. This is a syntactic definition, and a reserved word may have no user-define meaning.Ī closely related and often conflated notion is a keyword, which is a word with special meaning in a particular context. In a computer language, a reserved word (also known as a reserved identifier) is a word that cannot be used as an identifier, such as the name of a variable, function, or label – it is "reserved from use". Word in a programming language that cannot be used as an identifier