A trade magazine is a publication focused on a specific industry or trade. Most folks here on Everything2 would probably be most familiar with computer trade magazines that focus on things like Linux, Windows, networking, database design, server systems, or others that are designed to pass on information, how-to articles, interviews, and other topics of interest to those who work in the IT field.
Some folks also lump hobbyist magazines as a type or sub-genre of trade magazine. Music, computer artwork, web design, writing, and even ham radio pubs could be shown to have the same goals and methods used by trade magazines.
Some examples include computer artwork (ImagineFX), amateur radio (QRZ), writing (Writers' Journal or Writer's Digest), computer networking (MSIE or Network), and databases (Oracle).
Iron Noder 2017