relevancy is much important in seo. we need relevant link. link from relevant site is better, etc... but how to know if relevant? for example. my site is about world of warcraft(game). but site A is about EDO(game). so are the two site relevant(both are game site)? but both site have few word "game" in content? another case:site A is about football ,site B site about sport in general(with few football content). are site A and site B relevant?
search engines will check the keywords on both web sites. if both web sites contain the same keywords, those web sites are related according to the search engines