What is Page rank?

Google's foundational algorithm that determined a page's importance and prominence based on the quantity and quality of backlinks pointing to it.

From 12 Ways to Get Quality Backlinks by SpyFu Ep. 547

A Google metric named after Larry Page, not the term web page. More web pages on a site can increase its page rank potential, but improper internal linking can prevent a site from reaching that maximum.

From SEO Vs. Yellow Pages and Video Submission on YouTube - Unknown Secrets of SEO E-Webstyle Number 6

Named after Larry Page, it is a measure of a website's authority. More web pages on a site can increase its page rank potential, but improper internal linking can prevent a site from reaching that maximum.

From How to Avoid SEO Sabotage - Unknown Secrets of SEO E-Webstyle Number 7

Google's numerical measure of a webpage's authority and value, referenced in the episode when evaluating whether a reciprocal link partner is a high-quality or low-quality site.

From Specific Calls to Action to Convert Web Traffic, A Great Interview Part 4 of 4 - Unknown Secrets of SEO E-Webstyle Number 31

Google's iterative, algorithm-based measure of a page's global link popularity, influenced by the quantity and quality of external sites linking to it.

From Keywords and Twitter, What to do with both? - #seopodcast45