In the interface and in the help, "BibTeX field" is mentioned, while the field is not BibTeX specific (i.e. it could be a biblatex field too).
Here is an example from the group interface:

Like "bibtexkey" was replaced by "citationkey", I propose to replace "BibTeX field" and "biblatex field" (when the field is not specific to BibTeX or biblatex).
What would be a good replacement:

• bibentry field?
• bibliographic field?
• entry field?
• ...?