Database: A large, regularly updated file of digitized information (bibliographic records, abstracts, full-text documents, images, statistics, etc.) related to a specific subject or field, consisting of records of uniform format organized for ease and speed of search and retrieval, and managed with the aid of a database management system software.
Periodical: A publication appearing at regular (or irregular) intervals with its own distinctive title, containing a mix of articles, editorials, reviews, columns, short stories, poems, or other short works written by more than one contributor, issued in soft-cover more than once. Examples include journals, magazines, and newspapers.
Article: A self-contained nonfiction prose composition on a fairly narrow topic or subject, written by one or more authors and published under a separate title in a periodical containing other works of the same form.
Peer-Reviewed: Peer-review is a process that many scholarly journals undertake to evaluate the quality of the material being submitted. When an article is submitted to be published in a peer-reviewed journal, several impartial reviewers (who are experts in the subject matter) assess for accuracy and the validity of the research methodology and procedure. The article is written by a scholar/expert, is usually long (10+ pages), and has footnotes and an extensive bibliography at the end.
In order for an article can be peer-reviewed, it must go through a rigorous "process of critical evaluation by one or more experts on the subject, known as referees, responsible for...evaluating originality, quality of research, clarity of presentation, etc. Changes may be suggested to the author(s) before an article is finally accepted for publication. " (Taken from the Online Dictionary for Library and Information Science).
Click here to see a marked-up example of a peer-reviewed journal article. This will show you what to look for in determining if an article is indeed peer-reviewed.
Clicking on the "Peer reviewed" box when searching for articles doesn't work 100% of the time. Sometimes pesky articles that haven't been peer-reviewed sneak in! To make sure that the article you're looking at is peer-reviewed, check out Ulrichsweb to definitively determine if an article is from a peer-reviewed journal. Click on the title of the journal, and look for the referee icon as well as Academic/Scholarly for content type. An example is below: