Administrative law is conventionally defined as the law regulating the organisation, composition, functions and procedures of public authorities; their impact on the citizen; and the restraint to which they are subject. By public authorities is meant the State itself, the Government, a Minister in his Department, local authorities, State companies or corporations, and where applicable, officials of the State or of other authorities of a public nature who are given some function in which they are required to make adjudications.

Justice Brian Walsh

Administrative law (or regulatory law) is the body of law that arises from the activities of administrative agencies of government. Government agency action can include rulemaking, adjudication, or the enforcement of a specific regulatory agenda. Administrative law is considered a branch of public law. As a body of law, administrative law deals with the decision-making of administrative units of government (e.g., tribunals, boards or commissions) that are part of a national regulatory scheme in such areas as international trade, manufacturing, the environment, taxation, broadcasting, immigration and transport. Administrative law expanded greatly during the twentieth century, as legislative bodies world-wide created more government agencies to regulate the increasingly complex social, economic and political spheres of human interaction.

From: Wikipedia