Off-site SEO, commonly called “off-page SEO”, includes all marketing strategies that exploit the mechanisms that allow search engines toEvaluate authority of the content that is on your website - in contrast to on-page SEO, which optimizes the relevance of the content on your website. These strategies include, among others: acquiring links, obtaining customer reviews, content marketing on third-party platforms, etc.
Off-page SEO is the most often overlooked part of natural referencing by businesses. However, it includes among the most important among the 200 SEO factors known to influence Google's ranking of query results on its search engine. Some are luckier than others and naturally gain online authority because of the ultra-relevant, original and unique nature of their content on the web, but this is the exception.