The Danish flag is called "Dannebrog", [which is] old Danish for "The Danish Cloth".
As with many etymological questions, we have in fact two explanations for the origin of this term, and cannot know which is more correct. The Danish encyclopaedia says:
Navnet på det danske flag, Dannebrog, der betyder 'danernes fane' eller 'rødfarvet fane', forekommer første gang i en dansk tekst 1478 og i en nederlandsk tekst 100 år før; i den nederlandske våbenbog Gelre fra 1370-86 ses en rød fane med hvidt kors ved våbenet for Valdemar 4. Atterdag.
(Den Store Danske Encyklopædi, vol. 4, p. 453-4)
[The name of the Danish flag, Dannebrog, meaning 'banner of the Danes' or 'red banner', occurs first in a Danish text 1478 and in a Dutch text 100 years before; in the Dutch armorial Gelre (1370-86) a red banner with a white cross is seen next to the arms of Valdemar 4. 'Atterdag'.]
http://flagspot.net/flags/dk.html
