PageRank is used to determine the overall authority of a website on a scale of 1 – 10. PageRank score is also used to weight the value of inbound links. When this information was publicly available, it led to all kinds of black hat tactics such as selling links, spamming links, and so on.
Google will still be using PageRank score when determining how to rank content in search results, but individual webmasters will not have access to their PageRank score.
Google gave warning last month that this day would come, which was confirmed to SEJ via a Google spokesperson. We covered it with additional detail at the time, including how Google has been phasing out PageRank since 2013.