Organic Search Results
Organic search results are the results in a search engine's SERP that nobody paid to have shown. The algorithm ranks them purely on how well they match the query and its search intent, unlike the ads at the top with their "Sponsored" label. Ranking in those results is the core of SEO.
The result page has gained layers over the years. On commercial queries ads usually sit on top, and on many informational queries Google shows an AI Overview: a generated answer with source links that occupies the space above the classic results. Then come featured snippets, "People also ask" boxes, map packs on local queries and product carousels.
AI Overviews do not change the underlying mechanism. Google draws its sources from pages that already perform well organically, so the work that lifts a site in the organic results is also the work that gets it cited in the AI answer.
Most clicks from search engines still go to the organic results rather than the ads. An organic top position carries a kind of endorsement as well, since Google has judged this page to be the best answer, and that rubs off on trust in the sender. Unlike ads, organic clicks carry no cost per visit. How search engines settle that order is unpacked in the guide to search engines.