The Page Rank (PR) used to be one of the main methods used by Google. It was developed in the nineties by Larry Page and later Sergey Brin to be one of the main methods used by Google to determine a page’s relevance and importance. You can easily find your PR by downloading the Google Toolbar or by using one of the SEO tools you can find on the internet. It is a method based on various calculations that are far too complicated to try to explain them.
Even if the Page Rank is not as important as it used to be, some people still see this number going from one to ten as very important. It is very hard on the other hand to know how far your website is from the next Page Rank level.
A good website will still have a high Page Rank but it does not influence your ranking on the search engines any more.
The Page Rank of a website can still be used in Search Engine Optimisation (SEO) with especially link building and getting back links from other websites. It is said that it is better to go after high quality websites when you want back links going to your site. This is absolutely true but a good quality link does not necessarily mean a link coming from a website with a high Page Rank. Getting a link from a website with a Page Rank of let say six or seven or even 8 is always a great thing but it is even better to get links from website highly regarded in your industry, even if those websites only have a Page Rank of three or four.
An SEO company doing Search Engine Marketing or only Search Engine Optimization should know that getting inbound links from website that only have a Page Rank of let say seven is not going to be as effective as getting good quality links from industry related websites or at least from websites talking about your industry.
I noticed recently though that the country specific Google websites have a different Page Rank. For example Google Japan has a Page Rank of 9 whereas Google United Kingdom and Google China have a Page Rank of 8 and Google India has a Page Rank of 7.
It is very hard to tell why the Page Rank of those websites is different and many aspects can be considered.