"It's neither this thing nor the other" = Exactly what you have said (it's neither of them). --- Sometimes the expression "It's neither one nor the other" - which is often contracted in speech to: "It's neither one nor t'other" - is used by parents in the UK when it's not either child's fault (but, both of them have done something wrong). It's like saying that both children have done something wrong but neither of them have done something worse than the other. It's often used after children have had an argument/fight with each other and they're blaming each other. -- What you said is basically perfect though, I was just giving an example where it doesn't quite mean "It's not either of them". -- Take care and good luck! :)