The body of laws governing taxation WordNet 3.0 & Open English WordNet

Tax law or revenue law is an area of legal study in which public or sanctioned authorities, such as federal, state and municipal governments use a body of rules and procedures to assess and collect taxes in a legal context. Wikipedia

A binding rule or body of rules prescribed by a government stipulating the sum of money and manner of collection it demands for governmental support, facilities and services, usually levied upon income, property, sales or other financial resources. OmegaWiki

The area of law pertaining to the statutory and regulatory rules applicable to taxation. Wiktionary

Area of law. Wiktionary (translation)