Link development is nothing but linking your websites with other websites by means of Social Bookmarking, web directory submissions, link exchange and many more. If you want to increase your Page Rank and get organic traffic. Then link building is the key. The more link you generate the more traffic you will get. More Traffic = $$$
You need to have a quality links to your website, this has a big factor to increase the possibility that your website will appear in the search engines for a specifics keywords.
Backlinks are links that are directed towards your website. Also knows as Inbound links (IBL's). The number of backlinks is an indication of the popularity or importance of that website. Backlinks are important for SEO because some search engines, especially Google, will give more credit to websites that have a good number of quality backlinks, and consider those websites more relevant than others in their results pages for a search query. When search engines calculate the relevance of a site to a keyword, they consider the number of QUALITY inbound links to that site. So we should not be satisfied with merely getting inbound links, it is the quality of the inbound link that matters. A search engine considers the content of the sites linking to yours to determine the QUALITY of a link. When inbound links to your site come from other sites, and those sites have content related to your site, these inbound links are considered more relevant to your site. If inbound links are found on sites with unrelated content, they are considered less relevant. The higher the relevance of inbound links, the greater their quality and the more beneficial they are in getting your site ranked well in the search engine results Hope this helps