Directories and search engines provide a short description near each listing which aims to add context to the title.
High quality directories typically prefer the description describes what the site is about rather than something that is overtly promotional in nature. Search engines typically
- use a description from a trusted directory (such as DMOZ or the Yahoo! Directory) for homepages of sites listed in those directories
- use the page meta description (especially if it is relevant to the search query and has the words from the search query in it)
- attempt to extract a description from the page content which is relevant for the particular search query and ranking page (this is called a snippet)
- or some combination of the above