LER meaning in Military and Defence ?

Loss exchange ratio is a figure of merit in attrition warfare. It is usually relevant to a condition or state of war where one side depletes the resources of another through attrition. Specifically and most often used as a comparator in aerial combat, where it is known as a kill-ratio. For example, during the Korean War, American combat jets had a kill-ratio of 4-1. This means for every four aircraft shot down by an American aircraft, one American plane was shot down by an enemy fighter.