An imaginary line that connects points of equal height value eg the elevation of the land surface above or below a vertical datum, in this case of LINZ topographic mapping, this is Mean Sea Level.
Data Dictionary for contour: apps.linz.govt.nz/topo-data-dictionary/index.aspx?...
Although captured and presented at 1:25,000 this layer, for all intents and purposes, forms part of the Topo50 map series.
Further information on Topo50:
|Data type:||Vector linestring||Feature count:||136|
|Attributes:||GEOMETRY, definition, designated, nat_form, elevation|