• 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 range ballistic missiles in their terminal phase using a hit-to-kill approach.
• THAAD was developed after the experience of Iraq’s Scud missile attacks during the Gulf War in 1991.
• The missile carries no warhead, but relies on the kinetic energy of 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 detonate upon a kinetic energy hit.

Source:Wiki