Does a search engine index website or web pages ?
Search engines do not index websites, only index web pages. This means that when browsers come to your website, instead of indexing them all together, they look at each web page one by one and index them separately.
Now that you realize that not every web page is indexed by the search engine, that’s why all this matters. If you are optimizing your website for certain keywords, you must optimize each web page separately to rank on those keywords.