Persistent Uniform Resource Locator. A PURL is an URL with the persistence properties of an URN. PURLs were conceived by the OCLC as a transitional step toward the eventual standardization and use of URNs on the Web.
Weibel, Stuart, et al. "PURLs: Persistent Uniform Resource Locators." PURL. http://purl.oclc.org/OCLC/PURL/SUMMARY (12 Mar. 2001).