How many bells is a NMT worth?

Excuse me, I couldn't help but notice your mention of "NMT" and its value in terms of "bells." Could you please clarify what exactly an NMT is and in what context it is being valued in terms of "bells"? Is this a reference to a specific game, currency, or financial instrument that I'm not familiar with? I'm intrigued to learn more about this and how it's being used or traded.