What's the difference between a keyword and a reserved word?
For example, in the proposal for concepts in C++ one can read the following statement:
This proposal introduces five new keywords: concept, concept map, where, axiom, and late check. All of these keywords will also be reserved words.
Keywords have a special meaning in a language, and are part of the syntax.
Reserved words are words that cannot be used as identifiers (variables, functions, etc.), because they are reserved by the language.
In practice most keywords are reserved words and vice versa. But because they're two different things it may happen that a keyword is not a reserved word (e.g. a keyword only has meaning in a special context, and can therefore be used as an identifier), or a reserved word is not a keyword (e.g. because it is reserved for future use).
Update: Some examples as given by others that illustrate the distinction:
goto is a reserved word but not a keyword (as a consequence, you cannot use it at all)Just to show that the distinction is very meaningful:
Not in all languages are all keywords reserved words. In Fortran it is possible to do this:
if if then then else else
In this case, the keywords are not reserved, but depending on context can be interpreted by the compiler as variables.
A good example of this distinction is "goto" in Java. It's not a language keyword (i.e. it's not valid Java), but it is a reserved word.
It seems that the java designers are telling us "We're not going to use 'goto', and neither are you".
Wiki says this "A keyword is a word that is special only in certain contexts but a reserved word is a special word that cannot be used as a user-defined name."
http://en.wikipedia.org/wiki/Reserved_word#Reserved_word_vs._keyword
I guess keyword is a word used as "keyword" (like if, for, switch, etc...) while a reserved word is something you cannot use as variable name because it might become a keyword in a future version of the language.
Really it will depend a lot on context. For example, the ISO C++ Standard says that things like "if", "while", "int" etc. are keywords, and doesn't actually use the term reserved word, except once, in a footnote, where something else was probably meant :-)
The standard doe specify reserved names - for example, all names that begin with an underscore and an uppercase letter are reserved names.
Keywords : Keywords has some special functionalities to the compiler. So the keywords can not be used as identifiers in coding. Reserved words: Reserve words are the words which are reserved for future use. In java, const and goto are the reserved words which are not being used currently and may be brought back to java in the future. If we check here Java Language Keywords (https://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html) , It says that java (latest I guess) has 50 keywords including goto and const. So goto and const are the keywords which are reserved.
