The original Google algorithm. (Obsolete nomenclature).
The name of the original Google algorithm for inspecting a web page and assigning it rank in the form of a number from 1 (low) to 10 (high).
For several years, Google allowed anyone to query the PageRank of any given web page. This was discontinued several years ago. The SEO industry now must guess, and devise clever ways to test, to see what The Algorithm thinks about one method of providing structure and content, as compared with another.
Fortunately, Google does provide hints, now and then, so there are tea leaves to read, as well. We're not flying totally blind, here.