It's a common word used to describe things that are red in colour, like:
* Whero whenua - red soil
* Whero ika - red fish
* Whero rakau - red tree
It can also be used figuratively to describe things that are associated with the color red, such as:
* Whero ngakau - red heart (meaning brave or passionate)
* Whero matariki - the red star (referring to the star Antares)