Reference resources are a great place to begin your research. They can help you define terms as well as find overviews of topics and theories and identify keywords or alternate terms for database searching.
There are many different types of reference sources, which include dictionaries, encyclopedias, thesauri, bibliographies, handbooks, style manuals to name a few. The following list of titles is not an exhaustive but featured list of resources to consult.
Encyclopedia of Communication Theory
Encyclopedia of Communication and Information
Encyclopedia of Media and Communication
Communication, Cultural and Media Studies: the Key Concepts, 3rd ed.
P90 .H334642 2011 (Print, 4th ed.)
Encyclopedia of Social Movement Media
The Handbook of Media Audiences
Oxford Handbook of Internet Studies
Oxford Research Encyclopedia: Communication
Oxford Bibliographies provides peer-reviewed annotated bibliographies on film history, television studies, media studies, critical theory, visual arts, cultural studies, digital culture, game studies, popular culture and the study of the moving image.
Bibliographies are browseable by subject area and keyword searchable.
Take a look at the following subject guides: