An occupied dwelling is a private dwelling where at least one person lives on Census night. It counts as occupied if someone was home or usually lives there.
Most private dwellings are occupied. The share that is occupied matters because only occupied dwellings house people. A high rate means most homes are in use.
Place Forecast shows the split between occupied and unoccupied dwellings on the occupancy page. Occupancy rates are carried forward from the jump-off year to project how many private dwellings will be in use each year.