Where robots.txt controls crawling for the whole site, the robots meta tag controls indexing and serving for a single page. It comes in two forms: an HTML <meta> element, and an X-Robots-Tag HTTP header for non-HTML files.
The main directives
noindex, do not show this page in results.nofollow, do not follow links on this page.none, equivalent tonoindex, nofollow.nosnippet, no text snippet.max-snippet:[n],max-image-preview:[setting],max-video-preview:[n].noarchive,notranslate,noimageindex.unavailable_after:[date], drop from the index after a date.
The combination that fails
Blocking a URL in robots.txt and adding noindex to the page. Google never fetches the page, never reads the tag, and the URL can remain indexed. To remove a page: allow crawling, add noindex, wait for a recrawl, and only then block it if you want to.
Alien Road recommends: use data-nosnippet on specific elements rather than nosnippet on the whole page when you only want to keep prices or personal details out of a snippet. Suppressing the entire snippet reliably reduces click-through; suppressing one paragraph does not.