终端高空防御飞弹(Terminal High Altitude Area Defense, THAAD, 萨德)，前身是战区高空防御飞弹(Theater High Altitude Area Defense)，是美国陆军研发的一款拦截短程、中程和远程弹道飞弹的最终防御系统，属于美国国家飞弹防御署的一环，旨在拦截飞毛腿飞弹和同类的战术弹道飞弹。

战区高空防御飞弹的概念于1987年提出，于1990年初由美国陆军正式提出，美国海军也有类似的海基神盾弹道飞弹防御系统，后同归属于美国国家飞弹防御署，期望发展一种新的专用拦截用飞弹，防御覆盖面更广大，命中率更高，并能够拦截平流层上的飞弹。THAAD计划由洛克希德马丁公司作为主要承包商，主要分包商包括雷神公司，波音公司，Aerojet公司，Rocketdyne，霍尼韦尔公司，BAE系统公司，奥什科甚防御，MiltonCAT和Oliver Capital Consortium。

Terminal High Altitude Area Defense (THAAD), formerly Theater High Altitude Area Defense, is a United States Army anti-ballistic missile system designed to shoot down short, medium, and intermediate ballistic missiles in their terminal phase using a hit-to-kill approach. The missile carries no warhead but relies on the kinetic energy of the impact to destroy the incoming missile. A kinetic energy hit minimizes the risk of exploding conventional warhead ballistic missiles, and nuclear tipped ballistic missiles will not explode upon a kinetic energy hit, although chemical or biological warheads may disintegrate or explode and pose a risk of contaminating the environment. THAAD was designed to hit Scuds and similar weapons.