This idiom is used at Upper Intermediate level.
When a fact or opinion is neither here nor there, it is not important.
Words that have the same meaning (synonyms) of neither here nor there are unimportant, inconsequential, irrelevant and immaterial.
"The most important thing is that you take this medicine, and the cost is neither here nor there."
"Whether he goes to the party or not is neither here nor there as far as I'm concerned."
"I'm not interested in her opinion on this matter. Her views are neither here nor there to me."
