Page Rank is the SEO Website Ranking system of a particular Website Page, Website Article, any Web URL, the more is Page Rank of any website the more is SEO value of that website.
Page rank is no longer used by Google now, and it replaced with MOZ Page rank, Domain Rank.
Page rank (SEO PR Checker) in simple term is the Quality and Quantity of Website Backlink count, and it increases as your Backlink count increases.