Niue, a sovereign state in free association with New Zealand, uses two official legal tender currencies. The New Zealand Dollar is the circulation currency for daily transactions, while the government also authorises legal tender coins in the Niue Dollar currency for collector's purposes.
A number of mints issue a large variety of coins under the authority of Niue. Most of these are commemorative and collector issues dedicated to historical or general popular culture themes not related to Niue itself. Many of them are in standard bullion sizes - typically, one ounce of silver (abbreviated as 1 oz Ag, where "Ag" comes from the Latin word for silver, Argentum). Those issued at prices much higher than their bullion value are separately listed in the Non-Circulating Legal Tender (NCLT) silver ounce section of the site.
Unlike them, this coin is targeted at bullion investors and was initially released at a price close to the value of its precious metal content.
This is the sixth design in the Equilibrium series of bullion coins by the Pressburg Mint, and the first one issued for Niue (earlier issues were for Tokelau). The coins in the series have a new design every year and are about balance - equilibrium - between technology and humanity.
The Mint says about it:
The yin-yang is an especially important and popular representation of harmony, sprouting from the rich Asian tradition in philosophy. Equilibrium: a state in which opposing forces or influences are balanced. | 
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