A ridge, usually of rocks or coral, lying near the surface of the sea, which may be visible at low tide, but is usually covered with water
Data Dictionary for reef_poly: https://docs.topo.linz.govt.nz/data-dictionary/tdd-class-reef_poly.html
This layer is a component of the Topo50 map series. The Topo50 map series provides topographic mapping for New Zealand and it's offshore dependancies, at 1:50,000.
For some small islands the printed map scale is 1:25,000. Although presented at 1:25,000 this layer, for all intents and purposes, forms part of the Topo50 map series.
Further information on Topo50: