Oxford Dictionary of Plays
by
Michael Patterson
An International Dictionary of Theatre Language
by
Joel Trapido, Edward A. Langhans, James R. Brandon and June V. Gibson
Oxford Encyclopedia of Theatre & Performance
by
Dennis Kennedy
This series provides background information for many different styles and periods of theater. It is a highly recommended starting place when researching a new topic, and provides a great overview of the style, period, or genre in question. A few examples are below