A zone is an area whose temperature is controlled by either a thermostat or a mini split. During Flair app Setup, you'll be asked to add a thermostat or a mini split. Flair will create a zone for the device added.
Each room is associated with a zone. During Flair app Setup, when you create rooms, Flair will ask which heating/cooling device controls the room, and associate the room with the correct zone.
The zone is displayed in the room's settings. In the Flair app, tap the 3-dot menu on the room tile and select "Room Info".
This example shows the Room Info for a room called "Bedroom". This home has one zone called "Bedroom Split" that is selected to control this room.
This example shows the Room Info for a room called "Living Room". This home has an ecobee called "414 CRC" and we see this zone is checked.
In this same home, the "Dining Room" also has the "414 CRC" zone checked.