Any of 11 species of large flightless birds (ratites) native to New Zealand. All the moas are now extinct, but before being exterminated by the Maori this group included the largest birds to exist in historic times, including Dinornis giganteus, which stood taller than 2 meters at the shoulders when fully grown, much higher when it extended its long neck.
New Zealand lacks any large native mammals, and the moas grew to great sizes to fill the ecological niches usually taken by mammalian species such as buffalo, deer, cattle, etc. Some grazed the open grasslands in the manner of cattle but most lived in forest and browsed the trees and vegetation there. The only native predator capable of attacking a moa (and even then, only a small one) was the large Haast's eagle, also now extinct.
When the Polynesian Maori colonized New Zealand a millennium or so ago, they found the large, landbound birds no match for their spears, and soon hunted them to extinction. The colonists' canine and rodent companions would have found the moas' large eggs quite delicious as well, which probably accelerated the big birds' decline, as they reproduced quite slowly.
By the time the first Europeans encountered New Zealand several centuries afterward, the Maori had long exhausted their supply of easy meat. The moas were no more.
The extinction of the moas at the hands of the Maori is strong evidence against the myth of the so-called "noble savage." It's humanity that's at odds with nature, not merely Western civilization.
There is a New Zealand moa that's not yet extinct, however. The MOA project (Microlensing Observations in Astrophysics) carries out observations of a wide variety of astrophysical phenomena, using gravitational lensing to achieve great precision. Their homepage is at http://www.vuw.ac.nz/scps/moa/