PageRank
Google's original algorithm for judging a page's importance from the links pointing to it, named after co-founder Larry Page.
PageRank treats each link as a vote, weighted by the importance of the page casting it. It was the basis of Google's early ranking and, in evolved forms, link analysis remains part of it.
Google stopped showing public PageRank scores in its toolbar in 2016. Any "PageRank" number in a tool today is that tool's own estimate.