What does it mean?
A peer reviewed source has been examined and judged by other experts in the field prior to the editing and publication of a source.
How do I know?
Most academic books and/or those published by a university press go through a careful editing process and may be considered peer reviewed.
More commonly, you will be asked to look for peer reviewed articles. One easy way to search for only peer reviewed articles is to use a library research database that allows you to limit your search to peer reviewed sources, like this illustration from the EBSCO database Academic Search Complete:
Another option would be to visit the journal's/publisher's site and look for information about their review and publication process.
What isn't peer reviewed?
Regular web sites and blogs (ebooks and e-journals are possible exceptions, see above guidelines), newspapers and magazines, YouTube clips, popular reading, forum posts, lecture slides.
