As I have noted before, digital humanities is the merging of two areas of inquiry/activity that were once fairly distinct, humanities computing (also sometimes known as computational humanities) and digital media production. How and why the two got merged remains a larger history for someone else to unfold, but the folding appears to have occurred because they both take advantage of the immense processing powers of computers as both analytical devices, media production tools, and publishing platforms. A recent post on The Humanist by Sheffield University for their biennial Digital Humanities Congress has a nice formulation of all this:
Digital humanities is understood to mean the use of technology within arts, heritage and humanities research as both a method of inquiry and a means of dissemination. As such, proposals related to all disciplines within the arts, humanities and heritage domains are welcome.
The Humanist on-line seminar/mailing list archive is here.