In the past when a person wanted to publish an article in an academic journal they would send it off, the editor would send it to the referees, the referees wrote reports on this and then if it was OK. The editor would send the article to the printer, the printer then prints it and then sells subscriptions for the journal to the library. A person then goes to the library and reads it.
The new model (gold open access) is that a person writes a paper, they send it off, the editor sends it to the referees, the referees write reports on this and then if it was OK. The editor charges the author a fee and sends the article to the printer, the printer then prints it and sticks copies on the internet. A person then goes to the web or library and reads it.
If you want to know what I think of gold open access then read this, while I do not mind the idea of a journal charging a small fee such as £ 30 for a paper to cover some of the running costs, I think that large fees are unreasonable. I think that green open access is a better idea in many ways.
While some good open access journals exist, there are some very bad ones.
In this new model for journals sadly some bad “shark” journals have appeared, here is a link to a paper about these bad journals. Here is a link to a list of papers which J. Beall considers to be predatory.