The primary difference between a refereed journal and a magazine that is designed for the general public is that the articles in a refereed journal assume prior knowledge in a particular field. While the average person can read Time Magazine and understand it, Semiotics Quarterly is written primarily for people with advanced degrees in semiotics. This assumption of expertise allows writers to go into more detail and to discuss issues that wouldn't be of interest to readers of general interest publications.
"Refereed" is another term for "peer reviewed," meaning that people with expertise in the field read, edit and approve the articles that appear in the journal. Refereed journals may focus on medical, social or cultural issues, and each of them has reviewers who are specialists in their particular fields. This review process by experts is designed to ensure the quality and accuracy of the material that is published in the journal. Being published in a peer reviewed journal is a sign that a writer's work is accepted by her peers, and is usually a requirement in achieving a research or teaching position in academia.
Articles in refereed journals usually include footnotes and a bibliography. These features allow readers to check sources and to pursue further reading in the subject matter. In contrast, articles in popular magazines and journals, although they frequently involve research, almost never include footnotes because it isn't expected that readers will be checking on the sources that the author used. Peer reviewed journals are often read by other researchers who are working in the same field, so the ability to pursue sources is important.
Most refereed journals are associated with a university or a professional organization, and receive funding to cover their expenses. This means that they don't need nearly as much advertising as general publications, which depend on advertising for their survival. Many refereed journals have no advertising at all, while others may feature ads for books, conferences and other journals that are related to their field. Many professional and refereed journals don't pay authors for their work, which further reduces their operating expenses and thus their need for advertising.