The name applies to a series of guns, the first one officially called the 8.8 cm Flak 18, the improved 8.8 cm Flak 36, and later the 8.8 cm Flak 37.[N 1] Flak is a contraction of German Flugzeugabwehrkanone[3][N 2] meaning "aircraft-defense cannon", the original purpose of the eighty-eight. In English, "flak" became a generic term for ground anti-aircraft fire. In informal German use, the guns were universally known as the Acht-acht ("eight-eight")