Deep linking in search engine optimisation essentially means linking multiple pages together to interconnect the website articles and pages. Links to a website can be classed into 2 categorises, either a domain link, or an internal page link, a domain link refers to links pointing to the homepage e.g. http://www.domain.com/ and an internal page link refers to links pointing to inner pages of a website e.g. http://www.domain.com/product/
External Deep linking strategy:
It is vital that, as part of your SEO strategy, you should have links pointing to as many different inner pages as possible, and not just to the homepage e.g. http as this tells a search engine that you naturally have a website with lots of quality content on your websites homepage, as well as lots of quality content on internal pages, search engines also presume that you have a well structured website which people have found easily and consider it a useful resource.
Internal Deep linking strategy:
It is imperative to have, as part of your SEO strategy, a sound internal deep linking strategy, you should try to mention and link to older or relevant articles as from a users perspective it provides useful and related background information if they have not read it before, and from a search engines point of view it can help understand the structure and different levels of your website as well as increasing the website saturation by increasing the no of pages indexed by caching old pages not already in the index.
Conclusion:
A good deep linking strategy, can help search engine understand your website better and push up pages that have lost their authority to perform better for related natural searches, as when a new article links to a relevant older archived article using appropriate anchor text the link can provide more relevance the internal page, which will intern eventually pass some link juice back to the website homepage.
SEO Programmer
Vipul