[Q] Basic Terminology Questions

In order to get started on compiler design and implementation, I've been
reading various sources (including the FAQs for this newsgroup) and WEB
references. I keep running across a small set of terms that, evidently
everyone knows except me. [:-)


For example, in the JavaCC distribution there is a very simple grammar
called Simple1. In the description of this grammar (and the others, also),
the words "terminals" and "non-terminals" are used to name what, to my naive
eye, look like, well, simple rules.


Here's a couple of examples, both from the Simple1.jj file.


IGNORE_IN_BNF: {}
{
        " " | "\r" | "\t"
}


Why is the name, "IGNORE_IN_BNF", called a 'terminal'? Isn't this just a
rule to ignore white space characters?


Here's an example of a non-terminal:


void Input() : {}
{
        MatchedBraces() ("\n" | "\r")* <EOF>
}


In this fragment, the name "MatchedBraces()" is called a non-terminal.


Clearly, the terms terminal and non-terminal are meant to convey meaning.
Can someone tell me what both of these terms mean?


Thanks in advance


Cheers


Michael
[A terminal is a symbol that comes directly from the input, a nonterminal
is a symbol that is built up from zero or more other symbols. -John]

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