Is between the correct word when there are more than two items, for example 'a balance between a, b, and c'?

I know we can say, for example, "a balance between a and b".

Is it valid to say "a balance between a, b and c"?

Because I'm not sure whether "between" can be used for more than two items.
If not, what should be a proper word to use?

Answer

In your example, it's sooner a matter of collocations (set phrases/word combinations) with the word "balance" as in "the balance of animals and plants in the environment, the balance of advantage/forces/power".

There's no usage of the preposition "among" after the noun "balance", if that is what you mean. So, "the balance between a, b and c" is correct.

To see the difference between "between" and "among", you've already gotten the link, which is in the comment to your question.