What is a Periodical?
A periodical is any item that gets published routinely by a set period of time. It is published "period"-ically. Get it??
Those cycles have changed a bit now that we live in the Internet Age and information can be shared/published as soon as someone inputs it onto a web page. So newspaper items may be published via online websites (such as the Los Angeles Times or the New York Times) at any time throughout the day; same with items published on magazine web sites (such as Smithsonian.com or Time.com).
Even so, we continue to consider all the above-mentioned items--newspapers, magazines, and journals--to qualify under a large conceptual umbrella as periodicals.
As information passes through the Information Cycle, it gets packaged and distributed through different source types. Each of these sources can be useful in research, depending on your personal needs.
It can help in differentiating among the various types of sources to consider the audience that each one is intended for. Doing so helps you know if the source is considered to be popular or scholarly.
Informal communication is first to be encountered on the Information Cycle. This information is shared by individuals, including family members, friends, colleages, and co-workers, but the information is not necessarily fact-checked or confirmed for validity. Can include...
News articles are published for reading by the general public, so they're considered to be a popular resource. They can be published in smaller communities to provide local coverage, such as the Pasadena Star News, or they can be published in larger cities to provide national coverage, such as the Los Angeles Times.
Magazines are also published for reading by the general public, so they, too, are considered popular sources. You can buy them at grocery stores & newsstands, and find them in doctors' offices and libraries. Here are some you may already know: Vogue, Sports Illustrated, People.
Scholarly journals are published for a specialized reading audience of college students, professors, and top researchers. Since they are written by and intended for scholars, they are considered scholarly sources.
Books take the longest time to be produced and appear last on the Information Cycle, undergoing a detailed process of writing, editing, and publishing. Books may be written for a popular audience or a scholarly audience, and are often highly valuable as research tools, compiling the most information in one useful location.