Sites that include links to others sites as well as lists, including online retail stores. Directories are used to locate not retail stores, but also businesses online. For example you can use an online directory to locate a dentist or a doctor near you, or your nearest retail outlet for collecting goods that you have ordered online.
Online directories are very easy to use, and by simply filling out one or more fields in an online form you will receive the results that you are looking for in seconds. As the owner of a business, it makes good business sense to be registered with as many online directories within your niche as possible, the more places your details are available the more traffic that will end up at your site.