The term is "citation." In the citation you entered, U.S.C. refers to the United States Code, which is a compilation of every general permanent law Congress has passed that's organized by topic (and not by when it was passed). The US Code is developed by the Office of Law Revision Counsel of the House of Representatives, and is organized into (at the moment) 54 titles. The 29 is the title for the code section you cited; Title 29 deals with labor. Other titles include Title 10 (dealing with the military), Title 18 (crimes and criminal procedure), and Title 26 (income tax).
There are levels of organization below the title, but they vary by title (e.g. Title 29 is divided into chapters, while Title 10 has five subtitles, divided into parts, and those are divided into chapters). The level where the actual text of the law is found is the section; when you're citing something in the US Code, you cite it by title and section (§ is a standard symbol for "section"). So 29 USC § 203(b) is section 203 of Title 29, subsection B. You don't include the fact that it's in Chapter 8 in your citation, because title and section is all you need to find it.