Search Engine Optimization (SEO) is how your website gets found online. The better your SEO, the higher you ranking on Google and the more traffic you will get.
Google Analytics divides traffic that arrives at your website through a search engine results versus other channels like paid advertising or another website that links to yours. Non-paid traffic is known as organic search traffic.
Organic SEO is the term used to refer to methods to acquire a pure positioning on natural search engine results pages (SERPs).
Google and other search engines are constantly changing and adapting algorithms that could affect your search engine optimization efforts without you knowing.