What is 'readback' that govt said Ajit's pilots didn't give before crash?

Ajit Pawar's plane had been cleared to land on runway but pilots didn't give a readback of landing clearance to air traffic controller (ATC), government said. 'Readback' is repeating a message, in full or in part, to ATC to confirm receipt and understanding. It's critical during landing as it allows pilot and ATC to establish which runway is being used.