In the US, taxi time is included in flight time only if the taxi time was incidental to an intended flight. Taxiing only for the purpose of moving the aircraft on the ground does not count. Otherwise, the FAA does not strongly nor strictly define flight time.

Yes, in the world of professional aviation, taxi time is officially included in "Flight Time." According to the International Civil Aviation Organization (ICAO) and the FAA, flight time (often called "Block Time") is defined as the total period from the moment an aircraft first moves under its own power for the purpose of taking off until the moment it finally comes to rest at the end of the flight. This includes all time spent taxiing from the gate, waiting for takeoff clearance, and taxiing to the arrival gate. For pilots, this is a high-value technicality because these hours count toward their legal "duty time" limits and their total career experience. For a passenger, while you aren't "flying" in the air, you are "in transit," and the airline's responsibility for your safety begins the moment the tug pushes the plane back from the gate. This is why "on-time" arrivals are calculated based on when the plane hits the gate (Block In), not when the wheels touch the runway.