In many countries, the Yellow Pages refers to a directory of telephone numbers for businesses organized by the category of product or service. 

At least until the anti-trust breakup of the Bell System in the late 20th century, the term "Yellow pages" was a trademark for commercial directories and the commercial portions of the by-commercial-category sections of directories that also include by-name listings; directories were published on behalf of the component Bell companies by the Reuben H. Donnelly publishing company. Then and since, phone companies or their agents sell the right to place advertisements within the same category, next to the basic listings; since the Bell breakup, other companies (sometimes telephone companies who provide local telephone service only in areas not covered by the directories) publish directories that compete with those of local telephone companies for advertising business.