What is Public Law?

Legal Definition
Public law (lat. ius publicum) is that part of law which governs relationships between individuals and the government, and those relationships between individuals which are of direct concern to society. Public law comprises constitutional law, administrative law, tax law and criminal law, as well as all procedural law. In public law, mandatory rules prevail. Laws concerning relationships between individuals belong to private law.

The relationships public law governs are asymmetric and unequal – government bodies (central or local) can make decisions about the rights of individuals. However, as a consequence of the rule of law doctrine, authorities may only act within the law (secundum et intra legem). The government must obey the law. For example, a citizen unhappy with a decision of an administrative authority can ask a court for judicial review.

Rights, too, can be divided into private rights and public rights. A paragon of a public right is the right to welfare benefits – only a natural person can claim such payments, and they are awarded through an administrative decision out of the government budget.

The distinction between public law and private law dates back to Roman law. It has been picked up in the countries of civil law tradition at the beginning of the nineteenth century, but since then spread to common law countries, too.

The borderline between public law and private law is not always clear in particular cases, giving rise to attempts of theoretical understanding of its basis.
-- Wikipedia
Legal Definition
The laws that cover administration, constitution and criminal acts. It controls the actions betwen the citizens of the state and the state itself. It deals with the governments operation and structure.
Legal Definition
That branch or department of law which is concerned with the state in its political or sovereign capacity, including constitutional and administrative law, and with the definition, regulation, and enforcement of rights in cases where the state is regarded as the subject of the right or object of the duty,---including criminal law and criminal procedure,--and the law of the state, considered in its quasi private personality, i. e., as capable of holding or exercising rights, or acquiring and dealing with property, in the character of an individual. See Holl. Jur. 106, 300. That portion of law which is concerned with political conditions; that is to say, with the powers, rights, duties, capacities, and incapacities which are peculiar to political superiors, supreme and subordinate. Aust. Jur. "Public law," in one sense, is a designation given to "international law," as distinguished from the laws of a particular nation or state. In another sense, a law or statute that applies to the people generally of the nation or state adopting or enacting it, is denominated a public law, as contradistinguished from a private law, affeeting only an individual or a small number of persons. Morgan v. Cree, 46 Vt. 773, 14 Am. Rep. 640.
-- Black's Law Dictionary
Legal Definition
A public law is one in which all persons have an interest.
-- Bouviers Law Dictionary
Legal Definition
International law; criminal law.
-- Ballentine's Law Dictionary