Kiwi is the forex market's nickname for the New Zealand dollar, and for NZD pairs such as NZD/USD. The name comes from the kiwi bird, a national symbol of New Zealand.
Traders, analysts, and commentators use Kiwi for the New Zealand dollar generally, but most often for NZD/USD, which shows the value of the New Zealand dollar against the US dollar.
The Kiwi moves on Reserve Bank of New Zealand policy, interest-rate expectations, dairy export prices, commodity prices, Chinese economic data, global risk sentiment, and US dollar strength. New Zealand is a small, trade-sensitive economy, so the Kiwi reacts sharply to commodity and risk swings.
You see NZD/USD = 0.6100, so one New Zealand dollar equals 0.6100 US dollars.
If NZD/USD rises to 0.6200, traders say the Kiwi has gained against the US dollar. If it falls to 0.6000, traders say the Kiwi has weakened.