Definition of casualty
Many people mistake the word "casualty" to mean fatality. That's not the case. According to the DoD Dictionary of Military Terms, a casualty is Any person who is lost to the organization by having been declared dead, duty status - whereabouts unknown, missing, ill, or injured. See also casualty category; casualty status; casualty type; duty status - whereabouts unknown; hostile casualty; nonhostile casualty.
The wounded are also casualties, as are those missing in action. In essense, a casualty is someone who is no longer able to perform his/her military duty.