A professional journal or professional magazine is a collection of articles and images about diverse topics of applied science and professional news items. Usually these articles are written by journalists or scholars and are geared toward a public interested in science in general or in a specific field of applied science. Specialized magazines may also cover very practical information for professionals in the field of e.g. forestry, pulp and paper industry, electrical engineering, education etc. They are often published by professional organizations in these fields. Professional journals may cover very "serious" material, but to find consistent scholarly information you should use the scientific journals.
Professional journals, like scientific journals and newspapers, are called "periodicals" because they are published at regular intervals throughout the year.