“There is no universally agreed definition of a predatory journal or publisher. However, the predatory journals do not meet the global publication ethics standards defined by the Committee on Publication Ethics (COPE) and the World Association of Medical Editors (WAME)” -- Karen Holland, Prof. Peter Brimblecombe, Dr. Wim Meester and Susanne Steiginga.1
In December 2019, 43 participants from 10 countries, representing publishing societies, research funders, researchers, policymakers, academic institutions, libraries and patient partners (that is, patients and caregivers who proactively engage in research) have reached a consensus that predatory journals and publishers are entities that prioritize self-interest at the expense of scholarship and are characterized by false or misleading information, deviation from best editorial and publication practices, a lack of transparency, and/or the use of aggressive and indiscriminate solicitation practices.2
Historically, the term "predatory publishing" was started by Jeffrey Beall, a librarian from the University of Colorado, which refers to a questionable business practice of charging fees to authors to publish their articles without standard editorial and publishing services provided by legitimate scholarly journals.3 Please see the Wikipedia entries on Predatory Publishing and Predatory conferences.
In general, predatory journals exploit the Open Access publishing business model where authors are made to pay fees to make their work freely available to the public. The articles are not check for quality and the journals often fail to deliver meaningful editorial and peer review.
Publishing in a predatory journal could :
1. Holland K., Brimbblecombe P., Meester W. & Steiginga S. (2021). The importance of high-quality content: curation and reevaluation in Scopus. https://www.elsevier.com/research-intelligence/resource-library/scopus-high-quality-content
2. Nature 576, 210-212 (2019) doi: https://doi.org/10.1038/d41586-019-03759-y