Directory submission sites are those sites in which links of websites are submitted in order to gain PR. Actually in directory submission sites we submit links of our sites so that back links could be created. Back links are those links which help Google rank a site depending on number of backlinks and authority of sites where those backlinks are created. While creating backlinks we should consider certain criteria that those directory submission sites must be High authority mean that DR ( domain rating ) or PR should be high. DR is higher rating of a domain in a search engine which make a page or domain appear on top results of SERP ( Search Engine Result Page ). SERP is page where one asks a search engine i.e. Google or puts a query and a result displaying different results or links with relevant information on top positions depending on ranking of different pages or links. Another criteria we should also keep in mind while submitting a link of our website is that those websites should not be spammy otherwise we may face adverse results.
Here is a list of about 5000 site submission directory sites.