Indexing
Indexing means that Google has read, evaluated, and added a page to its database. Only then can it appear in search results. Being found and being indexed are two different things: Google can know about a page and still decide against including it.
The most common reasons for a missing index are easy to check. These include a noindex directive in the source code, a block in the robots.txt file, a canonical URL pointing to a different address, or simply insufficient content to warrant its own entry.
You can see the status in the Google Search Console under Pages. There you'll find not only how many addresses were included, but also the reason for each rejection.
A common misconception: A sitemap doesn't force indexing. It's a suggestion, not a guarantee. What really helps are internal links from high-quality pages and content that deserves its own URL.
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