SEO Legend and Terminology:

Ranks (Google and Alexa) - PageRank is Google's simple way of labling a page's importance. - A Pagerank starts at PR0 and can go up to PR10 for the most popular sites.
PageRank is a numeric value that represents how important a page is on the web. Google figures that when one page links to another page, it is effectively casting a vote for the other page. The more votes that are cast for a page, the more important the page must be. Also, the importance of the page that is casting the vote determines how important the vote itself is. Google calculates a page's importance from the votes cast for it. How important each vote is is taken into account when a page's PageRank is calculated.

Backlinks (links into the site from the outside) - This is another way to increase a site's total PageRank. The other is to add more pages. Where the links come from doesn't matter. Google recognizes that a webmaster has no control over other sites linking into a site, and so sites are not penalized because of where the links come from. There is an exception to this rule but it is rare and doesn't concern this article.

The linking page's PageRank is important, but so is the number of links going from that page. For instance, if you are the only link from a page that has a lowly PR2, you will receive an injection of 0.15 + 0.85(2/1) = 1.85 into your site, whereas a link from a PR8 page that has another 99 links from it will increase your site's PageRank by 0.15 + 0.85(7/100) = 0.2095. Clearly, the PR2 is probably better, but nothing is for certain.

Pages Indexed: This is simply the number of pages in a site that a service has decided to catalog. It picks and chooses which ones it likes, and does not index the others.

Directory Submissions: This is simply a part of this SEO system. It gives you the ability to submit your site to certain directory's. This often does very little for your rankings.