Traditionally a peer review system is organized by a journal to evaluate the quality of an article before it is accepted for publication. Peer Review in 3 minutes.
New ways of evaluating research are emerging along with new models for publication.
Also experiments are ongoing in new ways to recognize the work of peer review. Peer Review week 2016 focused on this; see #recognizereview
Peer review week 2017 theme was Transparency in Review
Some more examples: