Bison are a kind of wild cattle, very distantly related to domestic cows. There used to be millions of them living in America until they were essentially eradicated by human hunters in the 1700s. A few small herds survived this slaughter and there are some bison living still in national parks and on private land.
Bison are much larger and stronger than domestic cattle. The males, called bulls, can weigh up to 2,000 pounds. They are also much smarter than cows. Bison are very hard to contain, because they are large and strong and can break down fences. They are smart enough to pull open gates. They can jump six feet in the air and run very fast (about thirty miles per hour).
A lot of people call bison "buffalo", but they aren't buffalo. The difference is very complex, one of those things only scientists really understand, but bison and buffalo are not the same. They are two different families of cattle. When Europeans first saw the American bison, they thought it was something different and called it a "buffalo". Some people think that people started calling the American bison "buffalo" after hearing the French name for cattle, "beuf". We're not sure exactly why people started calling bison "buffalo", but now you know better and you will always call them by their proper name, "bison".
Bison breed in the fall, and the females have one beautiful little orange calf in the spring. Bison live in herds, usually lots of females and calves guarded by one adult male. When male calves get to be a certain age the adult male chases them out of the herd and they run off and join "bachelor herds" made up of young males. When the young males get older they will challenge adult bulls to win a herd of their own.