What is a circuit breaker in a stock market; how does it work?

Sell-off continued when the Indian markets opened for trade on Monday. The headline index S&P BSE Sensex tumbled nearly 3,000 points within the first 45 minutes of Monday's session as more countries went into a lockdown to stem the spread of fast-spreading novel coronavirus (COVID-19). In India, various state governments announced lockdown in nearly 80 districts across the country as the total number of confirmed Covid-19 cases inched towards 400.
 

Trading on the Indian stock exchanges was halted as the S&P BSE Sensex fell 10 per cent, triggering an automatic 45-minute halt. It was the second instance of trading halt in the