Periodic Call Auctions were introduced by SEBI in 2013 to reduce volatility in certain illiquid stocks. Illiquid stocks that meet specific criteria of illiquidity, as outlined in the SEBI circular, such as having an average daily number of trades of less than 50 and a daily trading volume of less than 10,000, among other conditions, are included in this category.
Stock exchanges shall identify illiquid scrips at the beginning of every quarter and move such scrips to periodic call auction mechanisms. To learn more, refer to BSE FAQ and SEBI circular here.