Google's numerical value (1-10) given to pages based on the quantity and quality of incoming links they've got vs the outgoing links on the page. It is easily faked and the PR displayed on the toolbar is not always accurate.
Improving Your PageRank- Include useful high-quality information on your site.
- Submit your site to various web directories and reference sites.
- Publicize your site to everyone with whom you communicate.
- Write a newsletter and send it out.
- Provide a Rich Site Summary (RSS).
- Ask other high-quality websites to link to your website.
- Provide motivation for highly ranked websites to link to yours.
- Check out a site before you link back.