Toolbar pagerank (aka TBPR) refers to the pagerank bar that is included in the Google toolbar. It indicates the value Google attributes to the web page currently being viewed. This is a different to the pagerank Google and other search engines use to rank pages in their search results.
While Google is the most popular search engine today, it was actually a relative latecomer to the world of search. Its rise to the top was driven by two major factors, the first was its clean interface containing little other than a search box and the Google logo, the other was pagerank.
Other search engines of the time found it difficult to judge the quality of any given web page. They could tell what a page was about by looking at text but there was no way of them really knowing if the information on that page was actually any good.
One of the founders of Google came up with a way of using links between web pages to gauge how accurate or useful a page was. In theory if a page contained accurate, useful information on a given subject, other websites would link to that page more than a page that was less useful. Google came up with a way of using links between pages to give each page a value or pagerank. The ideas was that the higher the pagerank = the more accurate and valuable the page = the higher that page should appear in the search results.
While modern search engines have grown far more complex over the years, pagerank is still at the centre of most major search engines and plays a key role in where a website shows up in the search results. As search engines became more popular, website owners were keen to make sure their websites listed as high as possible in the results. To satisfy some of the demand for information about a given pages pagerank, Google released a pagerank feature with their browser toolbar. The tool bar indicator would tell you the pagerank of the page you were viewing on a scale from 1 to 10.
While the pagerank indicator on the Google toolbar is still used, it has become widely accepted that the pagerank indicator in the toolbar is completely independent of the actual Google pagerank used to rank websites. While many webmasters still use it many take it as an approximate guide rather than precise measurement. To differentiate between the two values, the measurement on Googles toolbar is known as ToolBar PageRank (TBPR) and measurement Google uses to rank pages is simply PageRank (PR).