What do the terms crawler, indexing, referencing and ranking mean?
The crawl is the what makes robots when they browse a web page.
A web page is indexed when it is in the databases of search engines. We can also say that the page is referenced.
A web page is ranked when it is well positioned in search engines on given keyword with a qualified traffic-generating potential.
Chronologically, a web page is crawled firstly, then indexed and with some luck, ranked.
A non-indexed web page therefore never stands a chance of being ranked. Just so we're clear.
