A reserved
word is a word that is reserved for special use by the language. Reserved words are system identifiers and cannot be used by the programmer as a user identifier.
Technically a keyword is a reserved word that is currently used by the language with a special purpose.
Therefore all keywords are reserved words, however some reserved words are not keywords yet. The may be so at a later date.
For example, const and goto are reserved words and not keywords yet, they are reserved for later use.