The Zombie Stack Exchanges That Just Won't Die
Digital humanities (DH) is "analyz[ing] broad swathes of human experience in ways that weren't feasible before computers and digital materials" as well as applying humanities techniques to digital objects. For a more in-depth discussion, the current Wikipedia page is likely to have an up-to-date summary of this evolving field.
This tag is a general subject tag, describing a general field within the broad topic of "libraries and information science" that a question might fall into rather than necessarily describing something that the question is specifically about. For example, tei (the Text Encoding Initiative) is a specific standard within a sub-field of digital humanities; a question specifically about TEI might then be tagged both "TEI" and "digital humanities." (This practice is particularly helpful to those who might want to follow a single broad field tag rather than try to think of every specific item it might cover and follow all of them.)
Humanities computing is an older term for the field which became digital humanities.