Indexed pages are pages of website that have been crawled by Google and deemed to be of a high enough quality to appear in their search results for the appropriate keywords. When sites are crawled, Google captures the information on each page and if it is good enough, stores it in its directory. This means that the search results are not real time, they are a snapshot of the most recent information that Google holds at that moment; after the next Internet crawl, the results for your search could change.
The more in depth pages your website has the more pages will be indexed by Google. This is because Google looks for quality and so considers each page on its individual merits. Naturally, the more pages that make it into Google’s index, the more powerful your website will be and have a bigger chance at being displayed in the search engine results pages (SERP).