Website Links and SEO
Search engines put a great deal of importance on the number and quality of links that are pointing into a website to decide how relevant the information contained within is to the search results.
There are a range of link types and each are used by the search engines to return data about a website and its contents popularity amongst readers.
Global Links: A website which is globally popular and has thousands of links pointing into it (such as wikipedia) is viewed as the most important websites on a global level. The amount of links pointing into a globally popular website are what make it a trusted authority by the search engines.
Local Links: Local links are links from websites recognised as an authority on a topic that is relevant to the content of your website. Links which are on-topic are considered much more useful in determining the quality of your content than links from websites which are interested in completely unrelated subjects.
Anchor Text of a Link: One way that search engines determine how relevant your web page is to the subject that you want to get found for is by reading the text used in the anchor that links into you. When a large number of links use a relevant keyword in the anchor text when linking into you, it will give the search engine an indication of the content expected when you click through.