Collateral damage Collateral damage is damage to things that are incidental to the intended target . It is frequently used as a military term where it can refer to the incidental destruction of civilian property and non - combatant casualties . Etymology . The word " collateral " comes from medieval Latin " collateralis " , from " col - " , " together with " + " lateralis " ( from " latus " , " later - " , " side " ) and is otherwise mainly used as a synonym for " parallel " or " additional " in certain expressions ( " collateral veins " run parallel to each other and " collateral security " means additional security to the main obligation in a contract ) . The first known usage of the term " collateral damage " in this context occurred in a May 1961 article written by T . C . Schelling entitled " DISPERSAL , DETERRENCE , AND DAMAGE " . The " USAF Intelligence Targeting Guide " defines the term " [ the ] unintentional damage or incidental damage affecting facilities , equipment , or personnel , occurring as a result of military actions directed against targeted enemy forces or facilities . Such damage can occur to friendly , neutral , and even enemy forces " . Another United States Department of Defense document uses " Unintentional or incidental injury or damage to persons or objects that would not be lawful military targets in the circumstances ruling at the time . Such damage is not unlawful so long as it is not excessive in light of the overall military advantage anticipated from the attack . " Intent is the key element in understanding the military definition as it relates to target selection and prosecution . Collateral damage is damage aside from that which was intended . Since the dawn of precision guided munitions , military " targeteers " and operations personnel are often considered to have gone to great lengths to minimize collateral damage . Non - military uses of the phrase . The term ' collateral damage ' has also been borrowed by the computing community to refer to the denial of service to legitimate users when administrators take blanket preventative measures against some individuals who are abusing systems . For example , Realtime Blackhole Lists used to combat email spam generally block ranges of Internet Protocol ( IP ) addresses rather than individual IPs associated with spam , and can deny legitimate users within those ranges the ability to send email to some domains . The related term " collateral mortality " is also becoming prevalent , and probably derives from the term collateral damage . It has been applied to other spheres in addition to the original military context . An example is in fisheries where bycatch of species such as dolphins are called collateral mortality ; i . e . , they are species that die in pursuit of in the legal death of fishery targets , such as tuna . Controversy . The US military states the term is used in regards to unintentional damage , however , at least one source claims that the term " collateral damage " originated as a euphemism during the Vietnam War and can refer to friendly fire , or the killing of non - combatants and the destruction of their property . Also during the 1991 Gulf War , Coalition forces used the phrase ' collateral damage ' to describe the killing of civilians in attacks on military targets . According to Scottish linguist Deborah Cameron , " the classic Orwellian argument for finding this usage objectionable would be that In 1999 , " collateral damage " ( ) was named the German Un - Word of the Year by a jury of linguistic scholars . With this choice , it was criticized that the term had been used by NATO forces to describe civilian casualties during the Kosovo War , which the jury considered to be an inhuman euphemism . International humanitarian law . Military necessity , along with distinction , and proportionality , are three important principles of international humanitarian law governing the legal use of force in an armed conflict and how that relates to collateral damage . Luis Moreno - Ocampo Chief Prosecutor at the International Criminal Court investigated allegations of War Crime s during 2003 invasion of Iraq and he published an open letter containing his findings . In a section titled " Allegations concerning War Crimes " elucidates this use of " Military necessity " , " distinction " and " proportionality " : The U . S . military ' s approach to collateral damage . The U . S . military follows a technology - based process for estimating and mitigating collateral damage . The software used is known as " FAST - CD " or " Fast Assessment Strike Tool — Collateral Damage . "