Friendly fire is a fire from one's own side or allied forces compared with fire coming from enemy forces and widely put into used by the America military.
One side is to start a friendly fire with the intent of doing harm to the other side-the enemy. Friendly fire will not lead to a death resulting from a negligent discharge. Bothe murder and deliberate firing on one's own troops will not be regarded as friendly fire without intent to harm the enemy. Moreover, inadvertent harm to structures called as "collateral damage" does not define as friendly fire.
Friendly fire sometimes is referred to as blue on blue which derives from military exercises.
