Page Rank - PR 
Introduction
Pagerank, or more specifically Google Pagerank, is a value Google assigns to the individual pages of a website. The higher the Pagerank, the better.
The following article will discuss the various aspects of pagerank.
Value of PR
The PR of a page has a value. The value ranges between 0 and 10. 0 being the low end and 10 the higher end, or the holy grail of search.
The PR value of a page is visible to users who have the Google Toolbar installed with their browser. The toolbar has a green bar illustration of the PR for each page loaded up while browsing. The PR in the toolbar is said to be a snapshot of PR at a given period in time and is therefore not the current value.
There are a number of other tools providing users and webmaster with a way to assess their PR. One of these can be found at with this PR link.
Acquiring PR
PR is acquired by a site by the links pointing to the site in question. A link essentially being a vote, each vote having a value. PR is transferred, at a given rate calculated by Google, from one site to another and internally within a site. A link from a site with a high PR is usually better than a link from a site with a lower PR. Usually, because the number of outbound links on a page will affect the amount of PR transferred from one site to another. The more links on one page, the less PR that page transfers per link. PR is essentially divided by the number of links on the page.
PR is transferred within a site by the internal links to each page within the same site or domain. Folder structures also affect the transfer of PR with each sub-directory going down a notch.
PR and Search
PR directly affects the search results of a page for a given set of keywords. Times have changed recently with the weight assigned to PR but it is still an important factor in gaining good search results.
In the past, it was a given that if your PR was higher than another page and the pages were pretty much the same, the page with the higher PR would appear higher in the search results.
The above statement is not necessarily true these days. Lower PR pages do return higher in the results because of the affect of other variables of the search algorithm applied on the site.
Trusted PR
PR is also a handy measure to determine the trustworthiness of another site. It is a somewhat reliable signal of quality but should be used in addition to other methods.
Some sites appear to transfer more value than others with their links. For our purposes, we will call them trusted sites. Links from trusted sites are worth more in PR, relevance and effect than other sites. Seek these links out actively.
Summary
PR is a good thing. The higher the better. Search results are affected by PR to a certain extent. Seeing the little green bar go up after a PR update is fun, enjoy the ride!