The term collateral is used mainly to refer to something that is secondary, indirect, that is not the result of something intended but that arises as an indirect consequence. The term has been widely used in warlike circumstances to refer in a somewhat obscure way to the damage or casualties that a war can cause secondarily (for example, when innocent civilians are killed). The word is also commonly used in the cases in which it speaks of medicines that leave collateral or secondary effects, that is, effects that can arise indirectly.
The word collateral means, in other words, that something is secondary, that it is not direct. When you speak, for example, of a collateral entry, you mean that this is not the main entry. The term thus becomes a term in common use to refer to those things that are not central, that are not planned but that arise as an indirect consequence of a certain action. In this sense, the concept of collateral effects that a drug can cause is a concept that represents all those alterations or modifications that a substance generates in the body and that do not have to do with the main purpose for which it is consumed.
When we talk about collateral damage, we are referring to the damage that can be caused involuntarily or accidentally from an action that is aimed at generating other results. Thus, during the Iraq war at the beginning of the 21st century, the concept of collateral damage appeared repeatedly when trying to identify the dead and wounded, mostly innocent civilians of all ages, who were involuntarily produced by the troop action incorrectly. The concept was harshly criticized for considering that human victims can be understood as economic or material damage.
