Organic SEO is the phrase used to describe processes to obtain a natural placement on organic search engine results pages.
Some example of techniques used for organic SEO include using keywords and keywords analysis, backlinking, link building to improve link popularity, and writing content relevant for human readers.

To understand the organic seo term more easily, we can say the traffic we receive from Search Engine, other website due to backlinks, here in other website Facebook spamming in not considered because traffic from Facebook in considered to be a referral link rather than organic seo.
Organic SEO means getting found on the search engines without paying the search engines for the placement, and keep getting found for a long, long time.