Most of the periodicals you have encountered in life--magazines and newspapers available at the grocery store, airport kiosks, and convenience stores--are categorized as "popular" periodicals. That is, they have wide readerships, usually are (or are part of) for-profit businesses whose purpose is to increase circulation and sell advertising space, and they cover ideas, issues, events, personalities, and activities that have popular appeal.
You probably haven't ever run across Global Cosmetic Industry or Ink World at an airport kiosk. That's because they have very narrow appeal, targeting particular industries. They provide news about new products and processes, conferences and trade shows, and companies. Sometimes these are the only source of information about recent developments in business and industry.
The American Journal of Sociology and International Journal of Nursing Studies won't be making appearances at your local grocery checkout aisle. Journals like these, with circulations of two to four thousand, clearly aren't focused on wide appeal. They provide platforms for scholars to share groundbreaking research results that are often arcane and difficult to read for outsiders, and yet together form the foundation of substantive human knowledge about everything from abstract mathematics to zoology.