In searching PubMed and watching for “Free” articles, you’ll see the label “Free PMC Article” on many of them.
PMC, formerly known as PubMed Central, is a repository for research funded by the National Institutes of Health and for other freely available journal articles.
It can be searched as a separate resource as well as via references retrieved in PubMed. Since (unlike PubMed) it is a repository of articles rather than a database of references to articles, a term searched in PMC retrieves articles that mention that term wherever it appears in the text of the article. That makes it useful when searching some obscure issues, for instance, cases of a certain microbe causing a certain problem –
Search PMC directly using the pull-down option at the top of the PubMed page to switch from PubMed to PM
Typically, the PMC search on such a topic will retrieve more hits than in PubMed; some may be less focused, but since the text is immediately available, you can quickly open the article to check its content.