Organic SEO means that your website is optimized & promoted well in various search engines like Google, Yahoo, Bing following their mentioned guidelines for website marketing.
With natural SEO, there is no need for PPC advertising, paid inclusions, or any other similar techniques to try and deceive search engine rankings.
A Website that is optimized with organic SEO processes is likely to be more constant and effective in its SERPs ranking for a longer duration of time.