This guide focuses on electronic resources. During the Covid-19 quarantine, I also refer dance researchers to the New York Public Library special page on dance resources:
https://libguides.nypl.org/dance-division/remote-access
For the full Dance Resource guide, see https://guides.library.duke.edu/dance
Electronic
International Encyclopedia of Dance - Scholarly encyclopedia of just dance topics. Any word typed into this db will be related to dance. Also in hard copy.
Oxford Reference [Sources] Premiere - Performance - collection of scholarly online reference sources on the performing arts, includes the IED, above.
Duke Database list - the Duke Library's specialized databases limited to "dance" as a topic.
Encyclopedia of Esthetics - scholarly resource for the conceptual side of the arts, excellent for dance backgrounds & theory. This link places you in the Oxford Art Online database, simply select "Encyclopedia of Esthetics".
Books
International Dictionary of Modern Dance. Lilly Reference GV1585.B46 1998
International Encyclopeda of Dance (hardcopy)
Biographies
Biography Indexes (database group) - Sometimes professional biographies are better than the ones limited to 'dance'.
Music
Grove Encyclopedia of Music - scholarly encyclopedia of music and musicians. Includes world music and dances