Short definition
Rich results are enhanced search-listing features (review stars, FAQs, sitelinks, prices, breadcrumbs) Google generates from structured data on a page.
In depth
Rich results sit between plain blue links and full SERP features like the map pack. Eligibility requires correct schema, factual accuracy, and Google's quality bar. Common rich results for service businesses: sitelinks search box, review stars on the listing, breadcrumbs, FAQ accordion, and price snippets. Rich results lift CTR significantly — the SEO equivalent of curb appeal on a SERP listing.
Example
Adding Review schema with aggregateRating produces star-rating display under organic listings; CTR rises from 4.1% to 6.8%.