Periodical literature (also called a periodical publication or simply a periodical) is a category of serial publications that appear in a new edition on a regular schedule. The most familiar example is the magazine, typically published weekly, monthly, or quarterly. Other examples of periodicals are newsletters, academic journals and yearbooks. Newspapers, often published daily or weekly, are, strictly speaking, a separate category of serial. Periodicals are most often referenced by volume and issue. Periodicals have a set period and can be classified as popular and scholarly. Indefinite periodicals have an indefinite production cycle and have no plans to stop publishing. Periodicals use the International Standard Serial Numbers a standardized reference number. Periodicals often have a preferred and lower rate for postal distribution.