It is nothing but a practice of heavily targeting the same keyword phrase on multiple pages of a site.
This way search engines focuses on the web-site with full relevance to the main page. There is however no hard and fast rule that this should be done but it would be an added advantage in the aspect and development of search engine optimization.
This produces initiation in competition of search engine ranking and can produce a great deal in regular indexing and giving search engines an exact result instead of vague ideas.
Try it, I will yet be researching on topics such as this and giving my information in these blogs.
Cheers to Eukhost blogs,