basically the priest pronounces absolution without hearing the specific sins in a group.
That practice is condemned in the Catholic Church. There's an exception for instances where a group of folks is facing immanent and immediate hazard to life and limb ... but survivors are expected to make a regular sacramental confession as soon as possible.
Incidentally, we will often have something that goes by various names like "communal pennance service" which involves hearing a Scripture reading or two on the subject of repentance, a priest leading the faithful in an examination of conscience, followed by regular, individual confessions. Usually, several priests from nieghbouring parishes gather to hear confessions.