Meaning, it is perfectly normal for you to have a web site of 1,000 page and Google only index 900 or so of those pages.
Heck, even on this site, which has the best content quality of any site on the internet, Google has only indexed 95% of this site. That is I submitted 20,892 web pages and Google indexed only 19,928 pages.
It would however be nice to get a list of the pages Google has not indexed, like to filter out just those pages.
Here is John Mueller's tweet:
