Organic traffic refers to anyone who visits your website from unpaid sources, like non-sponsored Google search results. Organic traffic is highly valuable because it represents people who are actively searching for the keywords on your site and have a relevant and specific intent related to your business. This is the traffic that has the highest chance of conversion. The best way to increase organic traffic is through SEO.
See also: Paid traffic, Inbound marketing
Further reading: eCommerce SEO Strategies for Better Organic Traffic