NZ Post says on their web site:
In 1915 New Zealand’s role in the First World War reached a new level. In near-impossible conditions, the New Zealand Expeditionary Force took part in the Gallipoli campaign alongside our Australian neighbours. The Australian and New Zealand Army Corps (ANZAC) was formed and the spirit of Anzac lives on today.
That is where the word 'ANZAC' comes from, little known in other parts of the world but so famous in Australia and New Zealand. Ever since they fought together in Gillipoli there has been a close relationship between the two countries. More recently a closer bond has been formed with Turkey as well. In 1998 New Zealand and Turkey did a joint issue '1998 Memorial Statues - Joint Issue with Turkey.' You can find this in our collection, Military/ANZAC Part One.