What is nikah halala, over which a criminal case has been filed under UCC for the 1st time?

Nikah halala is a practice among Muslims, under which, a man cannot remarry his former wife unless she marries another man, consummates the marriage, gets a divorce and observes a period of separation. Uttarakhand Police have filed the country's first chargesheet under Uniform Civil Code in a case pertaining to alleged triple talaq and halala.