Dreidecker is the german word for triplane. This plane was extremely maneuverable and agile in the air. Richthofen called it 'machine gubs on wings'. A feared adversary in the 'air to air' combat in the first World War. 

It was introduced in July 1917 and in early 1918 it was already 'obsolete' compared to more powerfull and agile aircraft like the Fokker D VII.