Open Access is the free, immediate, online availability of research articles combined with the rights to use these articles fully in the digital environment. Open Access is the needed modern update for the communication of research that fully utilizes the Internet for what it was originally built to do—accelerate research.
- SPARC, 'Open Access'
Open Access publishing is when scholarly articles are published digitally on the open web, and there is no cost to the public to access / read / download them.
The articles in Open Access journals are openly-licensed: the article authors have agreed to voluntarily give up some of their copyrights to the general public - the open licenses make it clear to everyone what can (and can't) be done with the author's work without having to ask permission. To learn more about the open licenses used in OA journals, see this description by Creative Commons.
While online-only journals are not as expensive to run as a print journal, they still do require some funds for maintenance (website, storage, etc.). For this reason, there will often be a fee (Article Processing Charge, or APC) associated with having open access articles published. These funds may be paid to the open publisher by
Many grant funders require authors to publish the articles describing the results of their research in OA journals. To find out whether a publisher or a specific journal is open access or not, search for it by name on the Sherpa Romeo website.
Journals that publish work without proper peer review and which charge scholars sometimes huge fees to submit should not be allowed to share space with legitimate journals and publishers, whether open access or not.
- from 'Stop Predatory Journals'
Basically, 'predatory journals' are online journals that either take your money (APC) and don't publish your article at all, or do a lousy job of it - little to no quality control (such as peer-review and copy-editing). In other words... incompetent at best, grifters at worst.