A directory is a type of catalog, an organized list of people or businesses and how to contact them. If you need to find your lab partner's phone number, check the school directory.
An old-fashioned phone book is a directory, an alphabetical list of the people in your city or town, along with their phone number and address. These days such a directory is more often found online. In computing, a directory is also known as a folder, and it contains information about how data is stored in a computer. In the 16th century, a directory was a book of religious guidelines and rules. Directory comes from a Latin root meaning "to set straight."