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 commemorative and collector coins under the authority of Niue. These coins are dedicated to historical or general popular culture themes not related to Niue itself. Many of them are in standard bullion sizes - such as a half ounce of gold (abbreviated as 1/2 oz Au, where "Au" comes from the Latin word for gold, Aurum).
Note that the various mints have been authorised to use different effigies of the monarch, so the obverses are inconsistent.
The coins are "Non-Circulating Legal Tender" (NCLT) and not bullion because they are issued at prices much higher than their bullion value and are targeted at collectors who appreciate them for their artistic or sentimental value, and not at bullion investors.