What is noun modifier?

[whitemoon]

I want to know about noun modifier.
Some people say that the articles ," a, an and the" are noun modifiers. Are they right?
Others say that in the sentence,"A man in the car is my brother", "in the car" is noun modifier. Are they also right?
How many kinds of noun modifiers are there in English Language?

[Mister Micawber]

.
Noun modifiers can be premodifiers (a beautiful girl) or postmodifiers (the girl in the red dress).
They can be single words (one time), phrases (the man with the dreadlocks) or clauses (the girl who is sitting alone on the bench).
That's about it.
I would certainly call articles noun modifiers, as I presume that the general term noun modifier would include adjectives (beautiful, sesquipedalian), articles (a, an, the), demonstratives (this, that, these, those), possessives (his, my, John's), etc as subclasses.
.

[erinmcg]

I believe some of the other posters might be a little misguided concerning the formal definition of a noun modifier.

A noun modifier is actually anytime a noun is used as an adjective, as in a phrase like "baseball bat" or "gold bracelet". Baseball and gold are usually nouns, but they are acting as adjectives here, so they can be considered "noun modifiers", because thy are still nouns, but they "modify" other nouns (which is usually the job of an adjective).

This is the sole definition of a noun modifier.

[philo2009]

The previous contributor is right: precisely to avoid such needless confusion, the term 'noun modifier' is best avoided in favour of the much less ambiguous term attributive noun.

A word that modifies nouns is an adnominal, a category that naturally includes attributive nouns.

[macanudo]

It seems like this grammar point has many names. I did some quick research and it is also called an adjunct noun as well as noun + noun (by Michael Swan). I wrote up a quick article about noun modifiers, adjunct nouns, attributive nouns and noun+noun. It includes a few resources for exceptions to the rules.