thumb|upright=1.35|Diagram showing units "in enfilade" (red) and "in defilade" (blue) with another unit (green) providing enfilading fire
Enfilade and defilade are concepts in military tactics used to describe a military formation's exposure to enemy fire. A formation or position is "in enfilade" if weapon fire can be directed along its longest axis. A unit or position is "in defilade" if it uses natural or artificial obstacles to shield or conceal itself from enfilade and hostile fire. The strategies, named by the English during the Hundred Years' War, use the French enfiler ("to put on a string or sling") and défiler ("to slip away or off") spoken by English nobility of the time.
Enfilade fire—gunfire directed against an enfiladed formation or position—is also commonly known as "flanking fire". For instance, a trench is enfiladed if the opponent can fire down the length of the trench. A column of marching troops is enfiladed if fired on from the front or rear such that the projectiles travel the length of the column. A rank or line of advancing troops is enfiladed if fired on from the side (from the flank). Although sophisticated archery tactics grew rare in Western Europe during the Early Middle Ages, enfilade fire was reemphasized by the late medieval English using ranked archers combined with dismounted knights, first employed at the Battle of Dupplin Moor in 1332 and used to devastating effect against the French in the Hundred Years War.