Googlebot is Google's web crawler, the automated program that discovers pages by following links, fetches their content, and feeds what it finds into Google's index. Without Googlebot visiting a page at all, nothing about that page, however well-optimized, has any chance of showing up in search results.
There isn't just one Googlebot: Google runs separate crawlers for desktop and mobile (mobile-first indexing means the mobile version is the one that matters most for ranking), along with specialized bots for images, video, ads, and other content types. Googlebot respects robots.txt directives, reads meta robots tags, and executes JavaScript to render pages much like a real browser would, though that rendering step adds cost and can lag behind the initial crawl on JavaScript-heavy sites. Server logs that show Googlebot's actual visits, which pages it hits, how often, whether it's getting errors, are one of the more direct ways to see how a site is actually being crawled, rather than inferring it indirectly from indexing behavior.
