A flight of stairs is a set or series of steps between one floor or landing of a building and the next floor or landing. (floor usually means a landing). So, if the building had 5 floors, there would be 4 flights of stairs, one flight of stairs between the 1st and 2nd floor, the 2nd and 3rd floor, the 3 and 4th floor, and the 4th and 5th floor. The American and Canadian Building Codes do not specify the number of steps in a flight of steps, however, the codes do specify the height of the steps, e.g., 7.5 inches (19 centimeters).

"a flight of stairs" is a set of stairs going in the same direction. Typically, staircases consist of flights of stairs going in alternating directions and between flights of stairs are "landings". Same usage of "flights" in the UK.