Meaning of “law” - Learner’s Dictionary

law

noun us uk /lɔː/
They're lobbying for changes in the law.Both companies have insisted that they were acting in accordance with the law.Police officers are expected to uphold the law.It's against the law to leave young children alone in the house.He showed a flagrant disregard for the law.
the law

B2 the system of official rules in a country:

You're breaking the law.
It's against the law (= illegal) not to wear seat belts.
It's their job to enforce / the law.
by law

B2 If you have to do something by law, it is illegal not to do it:

They have to provide a contract by law.
RULE [ C ]

B2 an official rule in a country:

There are laws against drinking in the street.
They led the fight to impose laws on smoking.
law and order

the obeying of laws in society:

a breakdown in law and order
SUBJECT [ U ]

B1 the subject or job of understanding and dealing with the official laws of a country:

a law school/firm
ALWAYS TRUE [ C ]

something that is always true in science, mathematics, etc.:

the laws of nature/physics
the law of averages/gravity

(Definition of “law” from the Cambridge Learner’s Dictionary © Cambridge University Press)