Let's dissect what term organic traffic actually means.
Organic traffic is the flow of visitors arriving to a website from the natural (non‑paid) search results of search engines. Users type keywords or phrases into a search engine, receive a list of pages that match those queries, and click through to go to the sites. Those visits constitute organic traffic. It does not include traffic generated by contextual advertising.
Organic traffic is considered unpaid. Traffic generated by contextual advertising is paid.
It is generally regarded that organic traffic is of higher quality than paid traffic and tends to have a higher conversion rate as well as longer visit (session) time on the site.
Many users deliberately avoid clicking on ads and prefer to follow links from organic search results. While organic traffic is free, it requires a lot of work – for example content optimization, usability, and page load speed improvements.