Peer Review practically speaking refers to review for publication in a journal proving a way to find and correct mistakes before publication of a paper includes spelling, grammar, mathematical and other form of mistakes. It a method of quality control to the research being published helping guard against poor research.
Unfortunately this provides a means of blocking the publication of novel concepts that run contrary to the current paradigm. If dissenters respond be publishing their own peer review journals they are criticized and their journals are often decried as non reputable. Some times it is denied that they are even legitimate peer review. This has been shown too happened in origins research with Creation Science peer review journals and climate research with climate peer review journals that publish papers that go against Global Warming. So called reputable journals seemed to be defined based on agreement with establishment paradigms. Attacking sincere peer review efforts in this way harms scientific Research.