The way "common law" sounds and is used, I would have thought it meant law that is common (in common between) many countries, laws that can be found on the books in all of these many places. (Kind of like commonwealth.)

But, although it is common to many countries, that is not its defining characteristic. Its defining characteristic is actually something quite different.

Since the term is so far removed from what it actually means, I would even go so far as to say it is a mild euphemism.

Much better names for this exist: judicial precedent or judge-made law are the clearest options. But even "case law" is a better term.