PageRank is a rough estimate of the value that your website or webpage has in the eyes of Google. It's measured on a scale from 0 to 10, with 10 being the most valuable or relevant, and 0 being the least. For reference, consider that Google.com itself is basically the only site with a PageRank of 10, followed by sites like Yahoo.com at 9. In other words, don't expect your website to achieve a PageRank of 9 or 10 easily – or at all; for most websites, hitting a PageRank of 4 to 6 is very good.
So how does a website increase its PageRank? Though there are many factors which help determine PageRank, two of the major components are pages and links. Search engines like extensive websites with a lot of information, so a website with 100 pages would probably have a higher PageRank than a site with only 10. PageRank is also influenced by the links coming in to and going out from your website. In general, the more links from other sites that you have, the higher your PageRank.
PageRank is only one of the many variables that determine where your website shows up in natural search results, and it is only one of the things that a good SEO company will take into account. Having a high PageRank does not guarantee you good search placement, but it can help you get there.
Want to learn more about increasing your website's PageRank? Contact The Search Engine Guys at (512) 806-7955.