Wiktionary
d4
abbr. (context board games role-playing games English) A die#Noun with four sides. alt. (context board games role-playing games English) A die#Noun with four sides.
Wikipedia
D4
D4, D.IV, d4 or variants may refer to:
D4 (film)
D4 (or D4 Mortal Unit) is a 2010 horror film, directed and written by Darrin Dickerson. It stars Vicki Askew, Ella Bell and Eric Berner.