What counts as google index?

a page is 'in the index' when google has crawled it and stored it, so it's eligible to show up in results. being indexed doesn't mean it ranks, just that it can. easiest check is the url inspection tool in search console, it tells you straight. the pages report there shows which ones are left out and why. 'crawled, currently not indexed' is the one to look at on a small site.