Scholarly and peer-reviewed (or refereed) journals publish articles written by experts in that field for an audience of other experts and researchers. The difference between the two is that peer-reviewed/refereed journals review/critique the content of the articles using a panel/board of peers in that field before the article is accepted for publication. Most publications that are considered refereed will state so inside of their publication (usually on the table of contents page), on their website (look for a link to "about us"), and in Ulrich's Periodicals Directory (see the "title" section of volume 4, which is located behind the Reference Desk, and then look for the arrow symbol next to the title). Some of the library's databases allow you to limit your searches to scholarly articles and/or peer-reviewed articles, however...
Things like Letters to the Editor, Book Reviews, Commentary, News, items signed by anonymous, some or all of which may be found in an issue of a peer-reviewed journal, do not go through the peer-review process. Most of our databases have tools that allow you to refine your search to exclude this type of content from your list of results.