A Persistent IDentifier (PID) is a long-lasting reference to a resource. Often, a PID is associated to a set of metadata describing the object.
In the current scholarly communication environment, two types of PIDs are particularly extended, PIDs for objects (publications, data, software... ) and people (researchers, authors, contributors... ).
You can find a quick description of different identifiers here:
Please take a look at the introductory webinar: What are Persistent Identifiers and why are they Important? by Jonathan Clark
For a broad overview, read the ANDS Persistent identifiers awareness guide.
For an in-depth understanding of PIDs, take a look at the ANDS expert guide to Persistent Identifiers.
ANDS also has an excellent Webinar series on Persistent Identifiers.
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