rooms is defined in the first line. It’s a list of dictionaries. That’s iterating this:
{% set rooms = [
{
'name': 'A',
'cleaning': states('input_boolean.zone_a') | bool(True),
'area': 15
},{
'name': 'B',
'cleaning': states('input_boolean.zone_b') | bool(False),
'area': 10
},{
'name': 'C',
'cleaning': states('input_boolean.zone_c') | bool(True),
'area': 5
}
] %}