A casualty, as a term in military usage, is a person in military service, combatant or non-combatant, who becomes unavailable for duty due to several circumstances, including death, injury, illness, capture or desertion.
In civilian usage, a casualty is a person who is killed, wounded or incapacitated by some event; the term is usually used to describe multiple deaths and injuries due to violent incidents or disasters. It is sometimes misunderstood to mean "fatalities", but non-fatal injuries are also casualties.
In military usage, a casualty is a person in service killed in action, killed by disease, disabled by injuries, disabled by psychological trauma, captured, deserted, or missing, but not someone who sustains injuries which do not prevent them from fighting. Any casualty is no longer available for the immediate battle or campaign, the major consideration in combat; the number of casualties is simply the number of members of a unit who are not available for duty. The word has been used in a military context since at least 1513.
The military organisation NATO uses the following definitions:
In relation to personnel, any person who is lost to his organization by reason of being declared dead, wounded, diseased, detained, captured or missing.
Any casualty incurred as the direct result of hostile action, sustained in combat or relating thereto, or sustained going to or returning from a combat mission.
A person who is not a battle casualty, but who is lost to his organization by reason of disease or injury, including persons dying from disease or injury, or by reason of being missing where the absence does not appear to be voluntary or due to enemy action or to being interned.
These definitions are popular among military historians.
In relation to personnel, any person incapacitated by wounds sustained or diseases contracted in a combat zone, as well as any person admitted to a medical installation for treatment or recuperation for more than a day. There is a distinction between combat medical casualty and non-combat medical casualty. The former refers to a medical casualty that is a direct result of combat action; the latter refers to a medical casualty that is not a direct result of combat action.
A casualty classification generally used to describe any person killed by means of the action of hostile forces.
A casualty classification generally used to describe any person who has incurred an injury by means of action of hostile forces.
A casualty classification generally used to describe any person captured and held in custody by hostile forces.
While the word "casualty" has been used since 1844 in civilian life, it is a less important concept; the number of deaths on the one hand and serious injuries on the other are separately of major importance, and immediate availability for service is not. These numbers are usually cited together with or instead of total casualties.
According to WHO World health report 2004, deaths from intentional injuries (including war, violence, and suicide) were estimated to be 2.8% of all deaths. In the same report, unintentional injury was estimated to be responsible for 6.2% of all deaths.
Military Medical Casualties are losses during wars of armed forces personnel on account of wounds or other effects received from various kinds of weapons, as well as those who are admitted to aid stations or medical installations for more than 24 hours. Military medical casualties are one category of battle casualties, which also include what are called irrecoverable losses--those already dead or who die of wounds before reaching an aid station, those missing in action, and those taken prisoner. Military medical casualties usually greatly exceed irrecoverable losses--for example, the ratio was about 4:1 in World War I and about 3:1 in World War II. A distinction is made between combat and noncombat military medical casualties. The former refers to casualties that are the result of wounds, trauma, burns, ionizing radiation contamination, poisoning, and frostbite; the latter refers to casualties that are the result of noncombat injuries and diseases not related to weapons.