common law
Common law is law built not from a single written code, but from the accumulated decisions judges have made in real cases over centuries. When a court settles a dispute, its reasoning becomes a kind of guidepost — a precedent — that later courts are expected to follow when the facts are similar. So the law grows the way a path through a forest does: each traveler who walks it makes it a little clearer for the next.
This matters because it lets the law learn from experience and stretch to cover situations no lawmaker ever imagined. If your neighbor's drone keeps hovering over your garden, there may be no statute that names "drones" — but a judge can reach back to old rulings about trespass and nuisance and apply their logic to the new gadget. The rule "like cases should be treated alike" gives ordinary people some power to predict how a court will treat them.
A common misconception is that common law means "unwritten law" or mere custom. It is very much written down — in the published opinions of courts — and judges are bound by it. It simply lives in case decisions rather than in one tidy statute book, and it works alongside written laws passed by parliaments, which can always override it.
The system took shape in England in the centuries after the Norman Conquest of 1066, above all under the legal reforms of Henry II in the late 1100s, when royal judges traveling the country — the justices in eyre — began to forge a single body of law "common" to the whole realm. It later spread with the British Empire and today underpins the legal systems of the United States, Canada, and Australia, and strongly shaped the largely codified systems of countries like India.