More generally, the thing known as "common law": https://en.wikipedia.org/wiki/Common_law Note that "common law" does not mean "law that is common", at least not on an international scale; it is a specific legal system. As the Wikipedia article says, there are several others.
A super super high-level summary is that common law systems take more account of intent and precedent, whereas civil law systems tend to interpret the law exactly as written. A common law judge is more able to look at a litigant and take into account any sort of hypocrisy of their positions whereas I think a civil law judge in this situation would be more likely to simply take the case as is without such external considerations. But, let me again emphasize, that's a super-high level summary.