If you are familiar with the term "predatory publisher," you may have also heard of Beall's List, a list of purported predatory publishers.
The term "predatory publisher" was first coined in 2011 by librarian Jeffrey Beall. Beall identified a growing phenomenon: publishers and journals using deceptive publishing practices for material gain. These publishers and journals generally engaged in aggressive solicitation and made false claims about their editorial processes, while charging authors fees for publication. While Beall correctly diagnosed the problem, his solution (Beall's List) proved problematic for its biases against the open access movement and publishers from the Global South, as well as its lack of reproducibility.
It is for these reasons that we recommend against using Beall's List. There are more effective ways to avoid predatory journals and publishers. See the section above, "How can I avoid deceptive journals?"