Difference Between Periodical and Periodical Index?

What is difference between periodical and periodical index?

The difference between periodicals and periodical index is explained below:
Periodicals are the publications which are published in new edition after regular intervals. Newspapers, magazines, journals, yearbooks are the fine examples of periodicals.

Periodical index is used as a reference source for research. It provides you with the list of different periodicals and articles published in it. If you have any topic in your mind, a periodical index will help you to find the relevant piece of writing about that topic. It will help you in finding out the exact periodical (newspaper, magazine, journal etc) and its specific issue or copy. It is a kind of catalog which keeps the record of all periodicals for the researchers.