SEO is an abbrevation of Search Engine Optimization. During SEO process all pages are analayzed and studied and some new things are applied within the page and solely it is called as On Page Optimization. Search engine spider consideres all these changes while ranking your website for a particular keywords. Later on optimizer need to make his website popular. Making any website popular on web is done by creating some references on other sites. Creating such reference on other sites is called as Link Building.

Paid directories are best sources for link building as it saves time and quality check. Such directories are continously monitored by human and so there are very less chances of getting spammed. Paid directories are crawled very fast as compared to other free directories. It plays vital role if you opt for paid directory submissions.