Definitions:
Popular: Inform and entertain the general public. Magazines like Time or Rolling Stone; or newspapers like the L.A. Times. Written for a wide variety of readers.
Scholarly: Disseminate research and academic discussion among professionals in a discipline. Articles are written by researchers who are experts in their fields using the specialized terminology of the field. Almost always include the institutional affiliation of the author and a list of references at the end of the article. Usually peer reviewed.
Trade: Allow practitioners in specific industries to share market and production information that improves their businesses.