In many countries, the Yellow Pages refers to a telephone directory for businesses organized by the category of product or service. As the name suggests, they are usually printed on yellow paper, as opposed to white pages with non-commercial listings, printed on white paper. With the advent of Internet, the traditional term ‘Yellow Pages’ became applied to online directories of businesses.
The name and concept “Yellow Pages” were invented in the USA, over a century ago. The expression ‘yellow pages’ is used all around the world, in both English and non-English speaking countries. In the US, ‘yellow pages’ refers to the category, while in some other countries it is a registered name and therefore a proper noun.