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 weapons 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. The strategies invented by the English use the French enfiler ("to put on a string or sling") and défiler ("to slip away or off") which the English nobility used at that time.