Subject directories, also known as subject guides allow people to browse information by subject. They are hierarchically organised indexes of different subjects, with links to different web sites on each subject. The searcher can browse through the index in search of relevant subjects and navigate to the relevant web sites by clicking on hostspots which represent those sites: Subject directories are built by human indexers.
Apart from general subject directories, there are also two other types of directories specialised subject directories and clearing houses. Specialised directories specialise in their specific areas and provide access to the most important sites and resources in those areas, where as clearing houses are collections of various specialised search directories, either by including the search directory on their web sites or by providing a link to the web sites of these specialised directories. This facilitates easy location of specialised information on the Internet.