SEO is when you optimize your site to suit the algorithms Search Engines use the best.
Search Engines crawl the web 24/7, and their job is the find relevant information based on the input of an user. This process follows rules to determine the number in a list of results, based onthat number the site will be shown in result.
SEO uses techniques like, backlinks, to spread word of the page trought the Net.
Valid Page Markup makes it easier for crawlers to indentify and reate the contents of an website.
Keywords are used to tell the crawlers what to look for ono the page, while the title of an page also falls into this category, sames as the domain.
When someone uses keywords that are not primary but related for your page, the search engine uses backlinks to check for a possible information on the requested topic.
When you search on googe for:
php check memory
The first result will be a link to the PHP.net manualpage for the exact function to use.
http://php.net/manual/en/function.memory-get-usage.php
That's because every single tutorial has a link to this page, a backlink.
The 3 result is:
This page is rated the best besides php.net, means they have their site optimized well and they supply high quality content.
They also use a sitemap, when you look at
drupal.org › Support › Post installation, a crawler will nave no problems finding and indetifying the contents.