The "Four Freedoms flag" or "United Nations Honor Flag", influenced by Roosevelt's Four Freedoms, and intended to symbolize the WW2 Allies and their goals, as set down in the Atlantic Charter and the Declaration by United Nations.  This flag was designed by Brooks Harding in October 1942, and saw some use from 1943 to ca. 1948.  It was sometimes called the "United Nations flag", but was never an official organizational flag of the post-war United Nations.
For much more information, see World Flag Encyclopedia:  All World and Regional Flags Featuring Honor Flag Development 1942-1947 by Brooks Harding for the United Nations Honor Flag Committee (published 1948) OCLC 975401.  Also see https://www.fotw.info/flags/uno_honr.html , http://flagspot.net/flags/vxt-dv-h.html#honorflag , etc.

Image created by self from simple geometry.  Various proportions were in use, and there may not have been an exact "official" definition of the flag's geometry...
Original: Brooks Harding; United Nations Vector:  AnonMoos