While mostly important in the academic sense it seems appropriate to cover here as well: the consideration of what a peer-reviewed source is and why it may be important.
The basic concept of a peer-reviewed source is that a group of qualified people, usually recognized scholars of a particular subject, have looked at the information presented and compared it with what is already known or excepted about the subject. If the information presented doesn’t seem to fit with the commonly held understanding, then the information is looked into and verified.
When an article is published in a peer-reviewed manner there are extra sets of eyes that ensure validity. Most things published by Universities fall into this category.