What's a periodical?
A periodical is a magazine, journal, newspaper, or similar item that comes out periodically, i.e. once a week, month, etc.
It's good to be able to distinguish between scholarly and non-scholarly periodicals, especially for more advanced research. See the Scholarly Journals guide for more info.
To find out if a journal is considered scholarly, check the Ulrich's database by doing a search for the title of the journal.
If you see a little referee shirt icon then the journal title is considered peer reviewed "aka" scholarly.