CIWS stands for "Close-In Weapon System." It's a type of naval and land-based defense system designed to provide protection against incoming threats such as anti-ship missiles, aircraft, and other precision-guided munitions. CIWS employs rapid-firing cannons or Gatling guns along with radar or sensor systems to detect, track, and engage these threats at short ranges, typically within a few kilometers. The system's rapid rate of fire and accuracy make it a crucial component of modern naval vessels and military installations, providing a last line of defense against fast and maneuverable threats that may evade other defensive measures.