Friendly fire or non-hostile fire, a term originally adopted by the United States military, is fire from allied or friendly forces, as opposed to fire coming from enemy forces or enemy fire.
A friendly fire incident (fratricide), is when friendly forces or materiel are attacked and damaged by friendly fire which may be deliberate (e.g. incorrectly identifying the target as the enemy), or accidental (e.g. missing the enemy and hitting "friendlies"). Friendly fire is one kind of collateral damage. The term friendly fire is frequently used as a euphemism in military culture and frequently seen as an oxymoron.
The British military refer to these incidents as blue on blue, which derives from military exercises where NATO forces were identified by blue pennants, hence "blue", and Warsaw Pact forces were identified by orange pennants. Unofficially, the term 'own goal' is also used.