Persistent Uniform Resource Locators or PURLs can take many forms. Typically software that I use like WordPress has this functionality built in, but they call it by a different name Permalinks like the one for this article http://www.365webapplications.com/2009/12/15/what-is-a-purl, which you can see in your browser above. It is much more friendly than the database link http://www.365webapplications.com/?p=724. In SEO you want to sure you efforts don’t get lost over time, by using these in conjunction with search engine and human friendly names. Like http://www.365webapplications.com/category/review/, which regardless of the year would always show the latest reviews. Also archives would have similar forms like http://365webapplications.com/2009/10, meaning show all articles from October 2009.

These can be extended as tools by marketing teams to track sales and where they came from like advertised specials, which is most likely how a marketing consultant would use them. Like http://immersionit.com/new-year-special/ or http://immersionit.com/smb/, you see these all the time in ads from Dell, etc. This way it is easier monitor the success of the marketing campaign in both online and print media. This is generally a good idea, so in the future you invest in what invokes actions over what doesn’t. Of course it doesn’t stop people from being lazy and not typing the entire URL and skewing the results.

Update: Thanks Marty for pointing this out. In marketing the P can also stand for Personalized where the URL can be modified for a particular customer or prospect. My alumni association created one of these a couple weeks ago as part of a campaign for donations. The website then substituted my name throughout the copy, video, and images. It also allows you to make your tracking even more fine grained down to the particular recipient. (ie. http://giving.lehigh.edu/campaign09/jason.wood)

You can read more about Persistent Uniform Resource Locators on Wikipedia.