Since i talk about relevancy so much while talking about seo i think its time i explained how its built up.
You can judge a site’s relevancy in 3 easy steps.
Titles and Meta Tags
Take my blog for example, the titles and the meta tags have relevancy to each other as well as the niche, the keywords used in the title are also used in the meta tags, that helps in determining your rank in serps. Meta Keywords help in determining the page’s main subject/niche the description is what counts the most if you have the right terms used with the right context only then you can nail a good serp.
Titles however are not as important it gives you that special edge 
if you are going for a really big keyword, the title of this blog which is “Search Engine Marketing and Blogging Tips” is in perfect relevancy since i have my free seo book then my seo tips, on the blogging side i have my wordpress themes and the blogging tips, the titles and meta tags play a vital role in rankings because its how the site is classified you can have a home page with several keywords and descriptions and links or whatever but if your site does not have sufficient content for it, you won’t get a decent ranking.
The image below shows my explanation more graphically, landing a keyword is easy and having different keywords on the same domain is okay too until you can provide search engines with the content for it.
Internal links
Internal links hold alot of priority because serach engines like to see what people refer to your site as, if your site has 40% links with the title “SEO Blog” then you will do well on those serps and same with any other keywords you might want to target. Like i said before “You can have different keywords on the homepage as well…” that doesn’t mean you should get links for the homepage for all of those keywords, the keywords are there so that inner pages of your site may have good serps so if you get links directly to the pages that have the relevant niche you’ll find great results!
Outgoing links
Matt Cutts explained this in one of his videos, if Site A is based on health and health related tips and it starts linking to Site B which is a site promoting mortage loans and and finance, then that would be considered a bad neighborhood and their relevancy as well as SERPs will be shot this is what gets sites banned for paid links it has absolutely no link juice and no one is benefiting in that scenario.
Where as, if Site A is of a blogging niche and links to high profile sites within the blogging niche then that site/page will get more strength and probably a better rank in serps.
