PageRank is a Google numeric value that represents how important a page is on the web. Google figures that when one page links to another page, it is effectively giving a point for the other page. The more poings that are given for a page, the more important the page must be. Also, the importance of the page that is giving the point determines how important the point itself is. Google calculates a page’s importance from the points cast for it. How important each point is taken into account when a page’s PageRank is calculated.
PageRank is Google’s way of deciding a page’s importance. It matters because it is one of the factors that determines a Google page’s ranking in the search results. It isn’t the only factor that Google uses to rank pages, but it is an important one.