"Predatory journals" is a term attributed to a librarian, Jeffrey Beall, who began publishing a list of "predatory open-access publishers" in 2008. Beall wanted to name publishers who take advantage of the move towards open access and who use unscrupulous methods to obtain scholarly articles for their publications. Ttypically such publishers circumvent or distort the process of peer review and require the authors to pay APCs (author processing charges) in order for an article to be published. Beall stopped publishing his list in early 2017, having experienced great pressure from publishers he named and from some members of the scholarly publishing community because of the controversial views that he held.
Publishers do not have to use the guise of being "open access" to be classified as predatory. Nevertheless, there are steps that a scholar can take when looking for a journal in which to publish.