counter for houses, households, apartments
Used to count residential units. Often seen in addresses, real estate, and demographic contexts.
There are about two thousand houses in this town.
This apartment building has 50 units.
マンションの一戸を借りた。
I rented one apartment in the building.
About 100 houses are built in this area.
戸 counts residential units or households (often in statistics), while 軒 is the everyday counter for buildings, especially individual houses and shops.
The kanji 戸 originally means 'door' and came to represent a household or dwelling. The reading こ is the native Japanese kun'yomi.