Persistent uniform resource locator different from Uniform Resource Name
A persistent uniform resource locator (PURL) is a uniform resource locator (URL) (i.e., location-based uniform resource identifier or URI) that is used to redirect to the location of the requested web resource. PURLs redirect HTTP clients using HTTP status codes. 
Originally, PURLs were recognizable for being hosted at purl.org or other hostnames containing purl. Early on many of those other hosts used descendants of the original OCLC PURL system software. Eventually, however, the PURL concept came to be generic and was used to designate any redirection service (named PURL resolver) that:
has a "root URL" as the resolver reference (e.g. http://myPurlResolver.example);
provides means, to its user-community, to include new names in the root URL (e.g. http://myPurlResolver.example/name22);
provides means to associate each name with its URL (to be redirected), and to update this redirection-URL;
ensure the persistence (e.g. by contract) of the root URL and the PURL resolver services.PURLs are used to curate the URL resolution process, thus solving the problem of transitory URIs in location-based URI schemes like HTTP. Technically the string resolution on PURL is like SEF URL resolution.
The remainder of this article is about the OCLC's PURL system, proposed and implemented by OCLC (the Online Computer Library Center).