“Common sense” is a term that has more of a general meaning than any precise meaning that can be exactly and objectively defined. It generally refers to the way that any reasonable person would think. Therefore, its meaning is very subjective.
People typically talk about common sense as something that they have but which some other people do not. When they say that someone else lacks common sense, they are saying that the other person does not react to or think about common situations in a way that is at all logical. By contrast, a person who has common sense is the sort of person who thinks like them.
Common sense, then, is a very subjective term. A way of thinking that is common sense for one person or one group of people will seem like utter nonsense to another person. This means that we cannot truly define common sense in any way that is objective and that everyone can agree on.