2xx status codes are HTTP response codes that indicate a request was successful. The most common is 200 OK, which means the server delivered the page or resource as expected. Other 2xx codes exist, like 204 No Content for requests that succeed without returning a body, but in SEO you will most often hear about 200 responses because they confirm a page can be accessed normally by users and search engine crawlers.
In practical terms, 2xx codes help search engines crawl and index your site reliably because they signal that the content is available at the requested URL. To keep things clear and accurate, make sure important pages return a true 200 status when they should, and avoid cases where a broken or redirected page still returns 200, which can confuse crawlers and analytics tools. If you are auditing technical SEO, checking status codes is a straightforward way to verify that what you expect to be live and accessible is actually being served correctly.