Predatory publishers exist to profit off of research without regard for the peer-review process. The peer-review process might exist, but with an extremely fast turn-around time. Regardless of whether you are considering publishing in a traditional subscription journal, or an open access journal, or presenting at a conference, you should carefully analyze the journal or publisher for quality.
Resources for learning more about predatory journals or publishers:
From Think, Plan, Submit
Use the Think, Plan, Submit Checklist!