Indexing and Crawlability
Search engines need to discover a page before they can consider showing it. Discovery can happen through links, sitemaps, redirects, and external references.
Crawlability
A crawlable page is accessible to search engine bots. Broken links, blocked resources, login walls, and server errors can prevent crawling.
Indexing
Indexing means a search engine chooses to store and consider the page. Thin, duplicate, blocked, or low-value pages may not be indexed.
Helpful practices
Use clear navigation, submit a sitemap, avoid accidental noindex tags, and make important pages internally linked.