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A symbol or token is called non terminal when it does not appear in the resulting formal language.
They are derived token that are expressed via a rule with a regular expression that contains:
- either terminal token
- or other non terminal symbol.
- A token that is not terminal is a terminal one
- In a context-free grammar, Non terminal symbol appears on the left side of the production.
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Example
In a the following context free grammar
A -> a
A -> b
- The symbol A will never appears in the language.
- The language is composed of a and b but not A
A is then nonterminal symbol.