DOI stands for Document Object Identifier. This is a unique identifier that is assigned to an online journal article, online book or online book chapter. Most publishers assign these to their online content. A DOI can take you directly to an online resource, but JMU Libraries does not always have access at a publisher site.
Example DOI: 10.3390/ijms21031053
PMID is a unique identifier used in the PubMed database and can be used to look up abstracts in PubMed.
Example PMID: 32033398