What is convalescent-plasma therapy that has been approved by ICMR for COVID-19?

The Indian Council of Medical Research (ICMR) has given approval to SCTIMST, Kerala for carrying out convalescent-plasma therapy for COVID-19 patients. As part of the therapy, blood is drawn from a person who has recovered from coronavirus. The serum is separated and screened for virus-neutralizing antibodies. The convalescent serum is then administered to a COVID-19 patient.