"A process by which something proposed (as for research or publication) is evaluated by a group of experts in the appropriate field" (Merriam-Webster Online Dictionary, 2013).
Peer reviewed articles are appropriate for research papers because the information has gone through a process to ensure its credibility.
Many of our Herzing University Library databases include the option to limit search results to peer-reviewed materials. Look for a check-box to set this limiter when you are searching in the databases.