The sound comes from DayZ, the open-world survival game built around scavenging, player-versus-player combat and staying alive in a harsh post-apocalyptic world. The KA-M is one of its assault rifles, and a rapid burst from it has become a recognisable shorthand for sudden combat among DayZ players. Short clips like this one are widely shared on soundboards and reused in gameplay videos, streams and memes, where a few seconds of gunfire can instantly set the scene without any setup or explanation.