There are many definitions of "Digital Humanities" but all boil down to the application of digital tools or computational analysis to the study of the humanities.
CUNY A Day in the Life of the Digital Humanities (Day of DH) project
Brandeis University Library What’s “digital humanities” and how did it get here?
Matthew G. Kirschenbaum, ADE Bulletin What is Digital Humanities and What's It Doing in English Departments?
Anne Burdick, Johanna Drucker, Peter Lunenfeld, Todd Presner, and Jeffrey Schnapp A Short Guide to the Digital_Humanities
The British Academy: What are the digital humanities? by Professor David M. Berry