For a brief history lesson, according to Wikipedia, “Horse breeds are loosely divided into three categories based on general temperament: spirited “hot bloods” with speed and endurance; “cold bloods”, such as draft horses and some ponies, suitable for slow, heavy work; and “warmbloods”, developed from crosses between hot bloods and cold bloods, often focusing on creating breeds for specific riding purposes, particularly in Europe. There are over 300 breeds of horses in the world today, developed for many different uses. “
“The wild horse (Equus ferus) is a species of the genusEquus, which includes as subspecies both the domesticated horse as well as the undomesticated Tarpan and Przewalski’s Horse. The Tarpan became extinct in the 19th century, and Przewalski’s Horse was saved from the brink of extinction and reintroduced successfully to the wild. The most likely ancestor of the domestic horse was the Tarpan, which roamed the steppes of Eurasia at the time of domestication. Since the extinction of the Tarpan, attempts have been made to reconstruct the phenotype of the Tarpan, resulting in horse breeds such as the Konik and Heck horse. However, the genetic makeup and foundation bloodstock of those breeds is substantially derived from domesticated horses, and therefore these breeds possess domesticated traits.”
“The term “wild horse” is also used colloquially to refer to free roaming herds of feral horses such as the Mustang in the United States, the Brumby in Australia, and many others. These feral horses are untamed members of the domestic horse subspecies (Equus ferus caballus), and should not be confused with the two truly “wild” horse subspecies.” 
I have been fortunate to have witnessed a herd of wild horses when in Idaho a few years ago. This partiular herd was ecclectic. There were two obvious Thoroughbreds, both with evidence of presumably racetrack injuries. One appeared to have suffered a torn suspensory, the other a bowed tendon. Both got around well. There were two mares of what looked to be mixed breed. The term “grade” is often used as a description for these types of horses. Both had foals as their sides; the apparent offspring of the stallion leading the herd. They had his spitting-image head and roman nose.
I was on horseback, along with three other riders, so we were able to get fairly close to the herd. Our horses seemed confident at this presumably safe distance and vantage point, until the stallion raised his head high and stomped the ground. Three of our horses froze right on the spot, and one started backing up. We’d come as close as this stallion was going to allow.
One of the horses in the herd looked to be ancient, but quite content. All were in good flesh, even the old timer, respectfully. When one of the foals took a step in our direction, the stallion was the one to correct it, with pinned ears and a look. The mare then put herself between the stallion and the foal, and all went back to grazing. This was a small herd in comparison to some we’d heard of roaming this area. There was plenty of grass.
We turned and rode back to the ranch in awe. We hadn’t gone looking for a wild herd, but we found one. The locals in Idaho refer to this type of herd as “Mustangs.”
“A Mustang is a free-roaming feral horse of the North Americanwest that first descended from horses brought to the Americas by the Spanish. Mustangs are often referred to as wild horses, but the more correct term is feral horses. In 1971, the United States Congress recognized Mustangs as “living symbols of the historic and pioneer spirit of the West, which continue to contribute to the diversity of life forms within the Nation and enrich the lives of the American people.” Today, Mustang herds vary in the degree to which they can be traced to original Iberian horses. Some contain a greater genetic mixture of ranch stock and more recent breed releases, while others are relatively unchanged from the original Iberian stock, most strongly represented in the most isolated populations,” says Wikipedia.
“Today, the Mustang population is managed and protected by the Bureau of Land Management. Controversy surrounds the sharing of land and resources by the free ranging Mustangs with the livestock of the ranching industry, and also with the methods with which the federal government manages the wild population numbers.” 
The term “Mustang” seems to imply any horse running wild. I think if I were a horse, I’d want to be running wild. Even more importantly, I would want someone out there on my side, so that I could live out this life in the wild, unharmed. If I were domesticated and treated well, so be it. But recalling that herd, their contentment, their way of life, I think their biggest requests would be, please don’t hurt us. Don’t run us down with helicopters. Don’t mistreat us. Don’t cut off our water supply. Don’t sell us for meat. Please, just leave us be. “We thank you.”
 Horse – Wikipedia, the free encylopedia
 Wild Horse – Wikipedia, the free encyclopedia
[3[ Mustang – Wikipedia, the free encyclopedia