Does adding a comma before “or” change the meaning of a phrase?

Question

For example, the definition given from the OALD for pronoun is the following one:

a word that is used instead of a noun or noun phrase, for example he, it, hers, me, them, etc.

If I would rewrite it as the following, would the mean change?

a word that is used instead of a noun, or noun phrase, for example he, it, hers, me, them, etc.

If the meaning doesn't change, are there other differences between those phrases? Is this just an example of using the Oxford comma, or is there something different/more?

I am asking because I rephrase a similar phrase, and I was said it was more correct without the comma.

Answer 1

This is not an Oxford comma because it is not the serial comma customarily used before a coördinating conjunction at the end of a series.

It is instead an example of paired commas used as a weak or less obtrusive form of parentheses.

These are all equivalent:

1. A pronoun is a word that is used instead of a noun, or noun phrase, for example he, it, hers, me, them, etc.
2. A pronoun is a word that is used instead of a noun (or noun phrase), for example he, it, hers, me, them, etc.
3. A pronoun is a word that is used instead of a noun — or noun phrase — for example he, it, hers, me, them, etc.

Such “parenthifying” punctuation is something that could be omitted without great loss. I don’t think you can use the comma there, because “or noun phrase” cannot be freely omitted without changing the overall meaning.

Also, the indefinite article seems intended to distribute across noun and noun phrase in that sentence, and if you break it up with a comma, you lose that.

My own preference would be to write that this way:

• A pronoun is a word used in place of a noun or noun phrase; for example, he, it, hers, me, mine, and them are all pronouns.

Incidentally, this is the pro- that means “for”, so a pronoun is a word used for a noun (or noun phrase).

Answer 2

Regarding general usage (in the U.S., at least), I would encourage leaving out the comma.  For example,

You can have any kind of a pet except for a dog or a terrier.

is nonsense.  But

You can have any kind of a pet except for a dog, or a terrier.

means (or could be taken to mean)

You can have a pet cat, ferret, rabbit, or a terrier –– but not any other kind of dog.

So you may have introduced confusion into the other phrase where you added the unnecessary comma.