Are you asking about the 'E' or something else?
Quite possibly Eindecker, monoplane
A unarmed reconaissance aircraft
B two-seater, with the observer seating in front of the pilot.
C two-seater, with the observer in the aft cockpit.
CL fast two-seater, multi-role aircraft
D 'Doppeldecker', biplane. Later: fighter, in general
E 'Eindecker', monoplane.
Dr 'Dreidecker', triplane.
G 'Grosskampfflugzeug', bomber
J ground-attack aircraft
K 'Kampfflugzeug', later redisgnated with a G.
R 'Riesenflugzeug', long-range bomber.
http://www.warbirdsresourcegroup.org/LRG/classify.html
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