It refers to the two types of casualty in a battle or war. For instance, there might be 1000 casualties, wounded and dead, of whom 200 might be killed and 800 wounded.
In most common usage, casualties refers to people who are 'put out of action' , wounded, maimed or killed, by intent or by accident.
100s of Spartans were killed in many places, but the question probably refers to the Battle of Thermopylae in 480 BC, and the legend of the 300 Spartans.
I presume the question refers to the massacre which took place in 1890 at Wounded Knee in South Dakota and effectively marked the end of the US army's campaign to force native American tribes onto reservations established by the government.
All words have a part of speech. Casualties is a noun. It's the plural form of casualty.
The Western Front battle from July to November 1916 refers primarily to the Battle of the Somme, one of the largest battles of World War I. It was characterized by extensive trench warfare and significant loss of life, with over one million men wounded or killed. The battle aimed to relieve pressure on French forces at Verdun and to weaken the German army, but it resulted in only modest territorial gains for the Allies. The first day of the battle, July 1, 1916, remains one of the bloodiest in British military history, with nearly 60,000 British casualties.
THere was never a person called "Wounded Knee".The famous massacre that took place in December 1890 was not named for a person but for a small creek nearby - chankpé opi wakpála or Wounded Knee Creek in Lakota. This name existed long before the battle took place and probably refers to a long-ago fight between the Lakotas and another tribe such as the Crows, when a warrior on one side was wounded by an arrow in the knee.
"Wounded" typically refers to being injured or hurt physically. It can also be used to describe emotional or psychological distress.
The Holocaust
Battle execution refers to the commencement of battle.
The "battle" or "massacre" takes its name from a nearby creek, called chankpe opi wakpala in Lakota. This name, meaning "the creek of a wounded knee", was given to the stream (a tributary of White River) long before the battle, so it does not refer to any wound received during that famous encounter.It more likely refers to some much earlier fight between the Lakota and another tribe (perhaps the Crows).
"Casualty" refers to a person who is killed or injured. "Fatality" refers specifically to a person who is killed.