A floor is an area in indoor projects, on which you place content for your users to interact with. This is where you add and edit your floor plan and all of the information associated with it. You can add multiple floors to your project, but you need at least one floor and on it, you can put a floor plan graphic and stations that will appear on the top of the floor plan. If you skip the floorplan and just have stations, then the stations are shown as a list in the app.
Each floor would usually relate to a room in a building, multiple buildings in an area or the floors may be geographically unrelated.
See or FAQ post on How to add a Floor in an Inside project or watch the tutorial here.