Описание тега reserved-words
NoneReserved words are specific words in any language which are banned from use by authors, because of the special meaning they have in the language.
The language may have reserved words it is not currently using (Java has goto). While generally unwanted, new reserved words may also be added as the language evolves (since the version 1.5 Java treats enum as a reserved word, causing problems for the old code).
Some words that are commonly assumed as reserved are actually not reserved (for instance, it is ok to write int String = 1 in Java).