What is the S-400 system, India used to stop Pakistan's attack?

India used the Russian-made S-400 missile defence system to intercept Pakistani missiles after striking terror camps. The S-400, among the world’s most advanced SAMs, can target aircraft and missiles up to 600 km away. India signed a $5 billion deal in 2018 to acquire five S-400 units, enhancing its long-range defence capabilities.