PubMed - A service of the National Library of Medicine that provides access to over 17 million citations from MEDLINE and additional life sciences journals. PubMed includes links to many sites providing full text articles and other related resources.
PMID - PubMed Identifier. This is not sufficient for Public Access compliance
PMC - PubMed Central is a digital archive of life sciences journal literature, developed and managed by NCBI. With PubMed Central, NCBI is taking the lead in preserving and maintaining open access to the electronic literature.
PMCID - PubMed Central Identifier. This is the unique identifier for the PubMed record for a PMC article. The PMCID is needed for compliance with the NIH Public Access Policy.
NIHMS - NIH Manuscript System. If a journal article is not submitted to PubMed Central by the publisher, then the Reviewing Author to ensure complete submission to the NIHMS.
The PubMed Central reference number (PMCID) is different from the PubMed reference number (PMID). PubMed Central is an index of full-text papers, while PubMed is an index of abstracts. The PMCID links to full-text papers in PubMed Central, while the PMID links to abstracts in PubMed. PMIDs have nothing to do with the NIH Public Access Policy.