PageRank was one of the core aspects of Google’s original search algorithm (called Backrub), assigning a numerical value between 0 and 10 (10 being the highest value) to a page which would then significantly affect a page’s ranking in Google’s search results. Now considered to be a rather outdated ranking metric, it was based on PageRank or ‘link juice’ being passed between websites via hyperlinks. The higher the PageRank of the linking page, the more link juice was then passed to the destination page, subsequently increasing that page’s PageRank. It was based upon the concept of backlinks acting as votes or endorsements from one webpage to another, the higher your PageRank the more authoritative the page.
PageRank is an exponential figure, on a logarithmic scale. To put that in plain English, the difference between a PR7 link and a PR6 link is larger than the difference between a PR4 link and a PR3 link.
When PageRank actually mattered
PageRank was not the only ranking factor for website, but was nonetheless a significant one. It formed the core of a complex algorithm that also took into account factors already present in other search algorithms such as keyword matching. The objective was to increase your PageRank through other websites linking to your site, preferably with high PageRank themselves. It should be noted that if a page had multiple links on a page then the PageRank passed would diminish. Think of it this way: a page has a certain amount of link juice to pass. If it only has one link on it, the whole amount of link juice is passed to the destination page of that link. If it has two, then the two destination pages receive half each and so on.
The issue was that the numerical value of PageRank did not necessarily include quality indicators until Google unleashed their much feared Penguin. As a result, webmasters attempted to manipulate search rankings by acquiring links from thousands of PageRank 1 websites which, whilst individually would only pass a small amount of link juice, the theory was that with thousands there was strength in numbers.
Is PageRank relevant now?
I doubt many SEOs would now argue that the numerical value of your PageRank is of importance in today’s digital world. In fact, in 2014 John Mueller from Google has said that it is unlikely Google would update toolbar PageRank. The signs were coming for a while, toolbar PageRank was being updated progressively more sporadic and indeed the SEO industry was paying less and less attention to the metric.
So is PageRank dead?
Yes. A website’s PageRank will not be updated again (at least not visibly in toolbar PageRank). However, as a basic concept of a link acting as a vote or an endorsement still stands true. It is just that multiple other factors need to be taken into account and not every link will be taken into account. Most would argue that relevancy is of far higher concern in regards to link building and we would agree. The aim should always be to gain a link from the highest authority and most relevant website possible.
The problem with PageRank was that it was not discretionary enough. With updates like Penguin it became unclear as to whether these were add ons to the PageRank algorithm or stand alone sections. In reality we should view Google’s algorithm as one and take into account as many of their 200+ factors as possible. A website’s PageRank was a key metric for SEO in the early days of Google, but a single number to represent an algorithm with over 200 ranking factors was never going to work long term as Google became more and more complex.