Search engines keep a running keyword tally of which pages you have, who links to them, what they are about and how popular they are. If somewhere on some page in your site any two keywords exist then the crawlers have mapped it. If a link can be crawled and the page is still active, then it can be optimized or utilized for SEO to impact the collective world wide web.
The notion of popularity, being consumed by others seeking a topic, or stumbling across it by happenstance makes no difference whatsoever. Relevance is subjective and all that matters is that the page is in play. Somewhere between new, indexed, popular and forgotten, but none the less in play.
If it is in the index, it can rank for something (however abstract or precise) or potentially pass that ranking factor on to another page. Relevance boils down to subjective objectivity; on an algorithmic scale it equates to links, bandwidth and demand. Supply and demand leave a trail.
Popular documents and or websites create spikes in bandwidth forging a path of intent across social media networks, blogs, news sites, instant messages and all manor or electronic media.
Human or search engine user agent a.k.a. spiders know which websites, documents or pages have the knowledge or information people crave. It is through sharing with one another human to human, spider to human via search engine or or search engines taking preferences from humans is all part of the cycle.
From a technical standpoint, inverse document frequency IDF parses both the local term weights of your pages as well as globally parses their correlations in context to content (site wide) when consolidating the “similarity” thresholds to find a match for a query.
In other words
Based on the order of the keyword or key phrase and the parallels between the target pages “phrase” and / or “broad” match to natural language algorithm uses for normalization; an allocated measurement of relevance is assigned to each page based on a + or – lexicon.
Linking from a like to a like promotes an algebraic equivalent of relevance “to a themed consistency” throughout a website. Put simply, “ranked pages pass authority” to the target page via the link.
By using each page to target a slightly different keyword, synonym, singular or plural connotation of the semantic cluster “like a fuzzy set”, the “broad match” / overlapping nodes of relevance produce long-tail nirvana for a site (where the site ranks for a broad array of non-specific, loosely clustered queries) based on local and global proximity. This is the process of keyword stemming (a site ranking for more related phrases).
To bring a site back from the nebulous flash light / keyword cannibalized state, a healthy and consistent stint of inbound links can correct the “hanging in the 40’s” SERP result tendency and make pages buoyant where fluid rankings engage and can “break a page loose” from a ranking plateau and “complacent inertia”.
The value of link building is to see where the new found synergy tops out. Once it does, you refine the on page factors, add fresh content and see how the next round fares for that specific keyword or keyword cluster.
When a page is targeted with a smaller array of specific “inbound anchor text” then the easier it is for that page to rank for more competitive keywords.
Just Because You Forgot, Spiders Haven’t
The links from other sites align the on page factors to engage encourage a topical apex from dormant content. Pages you may have long since forgotten that have been aging in the background away from the spotlight can activate again and pass on some form of SEO ranking factor as a result of new inbound link flow – or take the spotlight as a new found ranking with a powerful internal or external link.
Through mapping out specific anchor text from external links and controlling a topically consistent internal linking tactic, a synergistic union can occur within a website that produces the proper mixture of elements to signify a high on page quality and / or relevance score.
In other words, titles, tags, meta descriptions, internal links, alt attributes anchor text, footer links, navigation structures can all be broken down to either contribute to or detract from relevant signals in search engines that either propel or inhibit rankings. Websites vacillate between signals or past, present and probabilistic future-tense thresholds.
Corralling that link flow requires knowledge of which ranking factors are passing value. The ranking factors could be past, present, on page, off page, present-tense or past-tense on page SEO / off page SEO or “all factors” such as (D all of the above) creating ripples simultaneously.
As you produce new content, the content from months ago emerges from the chrysalis of evolution, capable of reaching new heights in search engines with less dependency on the off page factor of links from other sites.
What this implies is, your website can produce its own rankings and its own ranking factor. So, before you give up and think that all of the content you may have tucked away in your website doesn’t matter, it is all tallied up instantly each time a search is conducted from a repository of crawled cloud data.
Just because you may have forgot about it, it is archived “just in case” someone searches for it, laying dormant in a non-preferential array. The good thing about archives is, that is essentially what a search engine is; a massive archive of moments captured in time and then parsed for relevance.
So, just like the masterpieces of the past, some things are too far ahead of the culture to be fully embraced “like many of the world’s most amazing musicians”… Search engines (since they are a reflection of the collective consciousness of the race) are also something which is alive, thriving, breeding awareness, data exchange and emotion as a result of the vast oceans of information.
But for now, the mechanisms are simple. What goes in, must come out, somewhere, some time from some one looking for something. Somewhere in between keywords, websites and all they contain are us on our vessels of individuality searching for relevance, time and time again.