What is circuit breaker, that Indian stock markets hit twice in 2 weeks?

A circuit breaker is a mechanism implemented by stock exchanges when they consider index movements to be excessively volatile. Circuit breakers in India are triggered when the Sensex or Nifty 50 breaches a pre-determined limit of 10%, 15% and 20% above or below their previous day close. Consequently, a market-wide trading halt is imposed depending on which limit is breached.