Frequency in keyword texts is a key SEO factor, said keyword density.
Web sites often come up with texts scattered with the same words. This is where the site owner tries to “push” some search engine terms in the hope of attracting traffic.
Google PageRank ™ is an indicator on a scale from 0 to 10 of the importance of a site.
The scale is non-linear, so between 5 and 6 there is a difference of significance much bigger than 0 to 1. Value 10 is very high and in the world there are 17 sites that reach it, including twitter.com and intel.com