Peer reviewed journals are well respected in the academic community. These are peer reviewed (sometimes called "refereed") to ensure the quality of the research articles in the publications. Most of these journals are published by reputable publishers or university presses.
See Wikipedia's featured article on Peer Review.
A periodical is any type of publication that is published at regular intervals in a series throughout the year such as magazines, journals, or newpapers.
This video is by Eli Moody from Vanderbilt University
This guide describes the differences between scholarly peer reviewed journals and popular magazines.
This video answers the question: "What is a peer-reviewed journal?" (Vanderbilt University, Peabody Library). After watching this video, you should be able to: