It refers to a place with a long stretch of water, like a river, stream, or even a long, narrow body of water like a lake.
This name is often used for places with long waterways, such as:
* Wairoa River: A river on the North Island of New Zealand.
* Wairoa Valley: A valley on the South Island of New Zealand.
* Wairoa, Northland: A town on the North Island of New Zealand.
The meaning of "Wairoa" can also be interpreted more broadly as "abundant water" or "place of flowing water".