Periodicals include articles in a magazine, articles in a newspaper, a review, articles in a scholarly journal, etc.
The basic citation for a periodical is below (from Purdue OWL).
Buchman, Dana. “A Special Education.” Good Housekeeping, Mar. 2006, pp. 143-48.
Krugman, Andrew. “Fear of Eating.” New York Times, late ed., 21 May 2007, p. A1.
Seitz, Matt Zoller. “Life in the Sprawling Suburbs, If You Can Really Call It Living.” Review of Radiant City, directed by Gary Burns and Jim Brown. New York Times, 30 May 2007, p. E1.
Duvall, John N. “The (Super) Marketplace of Images: Television as Unmediated Mediation in DeLillo’s White Noise.” Arizona Quarterly, vol. 50, no. 3, 1994, pp. 127-53.