Peer-reviewed articles, often called scholarly or refereed, are articles that are critiqued by impartial reviewers prior to publication. The reviewers are often anonymous and are considered experts in the field that the article/journal is published in. Reviewers are asked to judge the quality of the article by addressing the validity of the research, whether or not the methods chosen address the question(s) asked, and the accuracy of the data. If an article does not meet standards set by the journal it is usually sent back for revisions or is rejected for publication.
Some common characteristics of peer-reviewed articles are:
An article that meets one or more of the above criteria is likely to be peer-reviewed, however non-peer-reviewed resources may also have some of these traits. One example common in the animal science discipline is extension publications - while scientific in nature these often do not go under reviewed before being published and disseminated.
You can check to see if the journal your article is from is Academic/Scholarly and/or Peer-reviewed by using the Index - Ulrichsweb.com, (Remember there are only 5 simultaneous users, so if you can't access the index try again later).
Then click the Ulrichsweb.com link. Or just click the title link above.
Under "Quick Search" choose "Title" then enter the title of the journal (NOT the title of the article) into the box. Click the "Submit" button.
On the "Search Results" page click on the title of the journal.
Under the heading Document type: it should have Academic/Scholarly.
Under Refereed: it should have Yes.
If a journal is not peer-reviewed it will not have the heading Refereed at all.