AUD/NZD is the currency pair comprised of the Australian dollar and the New Zealand dollar. As the economies of New Zealand and Australia are closely intertwined, the two currencies tend to develop similarly against other currencies.
This means, for example, that NZD/USD will correlate to AUD/USD. Also, it means that the price movement of AUD/NZD will often be not very volatile.
The cross moves on the actual changes in the local economies, and is not heavily affected by risk-trends or global factors. Commodity exports represent a significant segment of both economies with Australia shipping energy products and ferrous metals; while New Zealand is more known for its export of wool, meat and milk.