The meta robots tag is a piece of code in the <head> section of a webpage that tells search engine crawlers what pages to index and follow links from, and what pages to ignore or not follow links from. It allows webmasters to control which of their pages are visible to search engines and whether internal links pass link juice between pages. The main functions of the meta robots tag are to determine what content search engines should index, what links they should follow, and whether pages should be included in search results or follow-up crawls.