In the library catalog, books, videos and other materials are assigned Library of Congress (LC) subject headings based on their content. Here is a sample list of theater-related subject headings, some of which pertain equally to books and videos (visual materials). When you view catalog records in discoverE, these subject headings display as active links pointing to other items with the same subject.
This is not an exhaustive list of subject headings pertinent to theater studies, but it should give you a sense of commonly used vocabulary and how subject headings are structured.
Sample Subject Headings
You can also search for individual playwrights and other people as subjects, as well as organizations such as theater companies. Here is an example: