What exactly are the city yellow pages?

"Yellow Pages" originated in North America, and the world's first yellow pages phone book appeared in the United States in 1880, with a history of more than 100 years. The Yellow Pages is an international industrial and commercial telephone book arranged according to the nature of enterprises and product categories, which is equivalent to the household registration book of industrial and commercial enterprises in a city or region. The international practice is to print on yellow paper, so it is called yellow pages. At present, we often say that the yellow pages refer to the telephone book. At present, almost every city in the world has a telephone book (yellow pages) printed on this paper.