Peer review is a staple of the scientific field, that in theory is an unbiased way to have members of the scientific community decide if new research is worth publishing. Anytime a scientist (or team of them) submits a paper to a journal, it goes through the process of peer review, a process that consists of many steps. The first step is an initial screening by the editor to make sure it’s a good fit (is it worth being published, does it fit the context of the journal, is it relevant, e.t.c), the paper could be rejected at this stage, although this is uncommon and would only happen to terribly conducted experiments or ones that are irrelevant to the journal. If the paper passes the first look-over, the paper will be sent to other scientists who are considered experts in the field, who will then determine if the paper is good to publish; they will almost always have revisions that must be made before publishing. After receiving a stamp of approval from the reviewers, the journal editor goes over the paper again to see if it should be published.
While this system may seem great at providing unbiased scientific discoveries, that sadly is not the case. Reviewers sometimes get to see the names of the people who are trying to get published, and personal biases can lead to them discrediting good work, or approving of shoddy work. This fault in the peer review system (along with a lack of transparency in most journals), is the major disadvantage associated with it.