Predatory Publishing was coined by librarian, Jeffrey Beall, who refers to PP as a questionable business practice of charging fees to authors to publish their articles without standard editorial and publishing services (in which they claim they provide) established by legitimate scholarly journals.
To simplify, predatory publishers purposefully mislead authors by promising peer-review services that they do not actually provide.
There are many types of behaviors that characterize predatory publishing practices. The following serve only as examples:
This infographic was created by the Canadian Association of Research Libraries.
Predatory publications: "Exploit the author-pays model of open-access publishing (Gold OA) for their own profit. With a false-front or non-existent peer review process, whether subscription-based or ethically-sound open access, these predatory publishers add little value to scholarship, pay little attention to digital preservation, and operate using fly-by-night, unsustainable business models." (Jeffrey Beale)
Hijacked journals: “A legitimate academic journal for which a bogus website has been created by a malicious third party for the purpose of fraudulently offering academics the opportunity to rapidly publish their research online for a fee.” (Butler, 2013a)
Sub-quality: Often mistaken for predatory publishers, they are not purposefully trying to deceive authors; however they can carry characteristics like grammar errors or lacks peer-review/solid publishing model.