Ius publicum is Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for public law

Public law

Public law is a theory of law governing the relationship between individuals and the state. Under this theory, constitutional law, administrative law and criminal law are sub-divisions of public law...

. It is to protect the interests of the Roman state (while ius privatum

Ius privatum

Ius privatum is Latin for private law. Contrasted with ius publicum , ius privatum regulated the relations between individuals. In Roman law this included personal, property and civil law. Judicial proceeding was a private process...

(private law

Private law

Private law is that part of a civil law legal system which is part of the jus commune that involves relationships between individuals, such as the law of contracts or torts, as it is called in the common law, and the law of obligations as it is called in civilian legal systems...

) concerned relations between individuals).Public law will only include some areas of private law close to the end of the Roman state.

Ius publicum was used also to describe obligatory legal regulations, such as ius cogens, which is now a term used in public international law meaning basic rules which cannot (or should not) be broken, or contracted out of. Regulations that can be changed are called today ius dispositivum, and they are used when party shares something and are not in opposition.