A search engine (such as Google) is just a website that is used to search for other websites. At the time of writing this article, the most popular web browsers are Chrome, Safari, and Firefox (in descending order). There is no central registry of all web pages, so Google must constantly search for new and updated pages and add them to its list of known pages. While some SEO tool companies have made a name for themselves pushing this concept forward, Google will be the first to tell you that it simply doesn't exist.
Because Google classifies web pages and not websites; therefore, those web pages can be in a subdomain or in a subfolder, and Google would treat them the same way. Google doesn't guarantee that it will crawl, index, or display your page, even if it follows the requirements of Google Search Essentials.