The library card catalog is an index because it lists the materials in a library and tells where they may be located. An index within an individual book lists the subjects and names mentioned in the book with a page number. These indexes are usually located in the back of the book. A basic knowledge of each of these indexes is necessary for you to be able to take advantage of all that the library resources have to offer. Everything else is secondary literature.
Periodicals are literary works published at regular intervals.
They include magazines and journals. Magazines are designed to appeal to a broad segment of the population. Journals are intended for a limited readership. The articles are written by scholars or experts in the subject area. The vocabulary is usually technical and often represents the author's personal research.