avant-garde (n.)

(also avant garde, avantgarde); French, literally "advance guard" (see avant + guard (n.)). Used in English 15c.-18c. in a literal, military sense; borrowed again 1910 as an artistic term for "pioneers or innovators of a particular period." Also used around the same time in a political sense in communist and anarchist publications. As an adjective, by 1925.

The avant-garde générale, avant-garde stratégique, or avant-garde d'armée is a strong force (one, two, or three army corps) pushed out a day's march to the front, immediately behind the cavalry screen. Its mission is, vigorously to engage the enemy wherever he is found, and, by binding him, to ensure liberty of action in time and space for the main army. ["Sadowa," Gen. Henri Bonnal, transl. C.F. Atkinson, 1907]