Online and offline directories are used by people who are looking for a person, business or other organisation. They are listed that are populated based on the information about the person or business that is being searched for. To make using these directories easier there are now many directories that are for a specific area, for example a business directory.
As you would imagine it is much faster to use an online directory as the search will be completed automatically for you. An offline directory is more time consuming to use as it will involve a manual search through the lists.